Have you come across SPACE at all? It might be helpful for your elder DD. I would imagine that some of her unpleasant behaviour is lashing out or rigidity in the moment related to dysregulation/anxiety/discomfort, which is ideally something she would learn not to do and (again ideally, because it's not always this simple) that you should probably aim to not accommodate, although in the short term it can be comforting to understand that it's not likely to be personal or literal. This is really tricky to manage because obviously you don't want them to feel worse, if the cause of their behaviour is them feeling bad. But OTOH the general world won't be especially understanding to any of this. Nobody outside of you, really, will care WHY she is saying/doing something unpleasant or be willing to see the underlying emotion rather than the behaviour. I don't know if there is any kind of course or therapy that would be useful in helping you work out how to navigate this, you could try investigating SPACE, NVR, CPV courses etc. (Although she is not being physically violent, the "vicious" verbal responses to you are along the same lines). She could probably find some therapy (e.g. CBT, DBT) to help herself control and stop the responses or redirect them into something which does not impact on other people, but the problem with this is that there's no point putting her into therapy if she does not want to change this behaviour. SPACE is designed to help even if the child/YP is refusing to engage, because the only thing you change is your own response. But I don't know if it would be right in this case. However it's very easy to find information about it so well worth looking up.
But then the second thing is that if she is feeling dysregulated/anxious/uncomfortable, that is likely to cause her to misinterpret and skew incoming information, so it could be that she genuinely feels aggrieved and hard done by and isn't able to recognise that this is completely out of proportion to what has actually happened, because it does feel in proportion to her. This is something where medication can help, particularly antidepressants can actually directly affect this kind of perception bias, so it might be worth encouraging her to see a doctor about checking whether her current medication is right for her (are the meds GP or psychiatrist prescribed?) but also ADHD medication sometimes seems to help with this, my vague understanding of it is that it's likely to either be a passive effect, because the ADHD meds alleviate some of the massive executive functioning load which comes with untreated ADHD and leads to exhaustion and burnout. Less exhaustion = less mood dysregulation. And/or, it increases functioning of the emotional "brakes" which allow us to tone down an emotional response from "OMG IT'S A FUCKING DISASTER" to "Oh, that's mildly annoying" as appropriate.
One last thing to add - DS2 is much younger, I do have a 17yo as well so I'm not new to this but it's DS2 who can be explosive in this way - but his can be very similar when he is generally under a high level of stress, and one thing which tends to help with managing it is to have an extremely clear and predictable system of minor sanctions plus clear rules/boundaries (for myself) as to when/how vs when not to engage, and to try as much as humanly possible not to go outside of this, and always to stick to it.
Removing the headphones as you did, I completely understand why you did that and it is logical. But it is the exact kind of thing that DS2 would not understand, and would get more and more wound up by, because it is something decided in the moment, essentially as a retaliation. It's not part of an established response pattern to behaviour. I did the exact same thing the other day - both DS2/3 were arguing about who got to use a console first, and I said they needed to discuss it and agree, which I was prepeared to referee, but because he was all wound up from school and couldn't reach a conclusion in the first 10 seconds, DS2 thumped DS3, so I snapped fine, you've lost your chance, DS3 can go first. DS2 you've lost screentime, you can maybe play later. DS2 has now been fixated on this for the last 3 days, trying to make sense of it because it makes no sense to him, trying to make sense of "If you get hit, then you automatically get first console access" or the perceived unfairness that DS3 "always" gets to go first. At the time that I said it, I was trying to say that punching is not a discussion, it is also not allowed, and since he refused to discuss calmly he lost the chance to have his time, but it wasn't clear at all and it was outside our usual system. I could have twisted it and said OK it's because you lost screen time, which is a usual sanction, but he knows that's not really what I meant in the moment, even if it was part of why it felt like a fair consequence to me at the time.
So bearing in mind it is extremely easy for me to sit here calmly and type this response and I know very well it is not easy at all in the moment, here's an idea of how a more structured response might look.
Last night there was a total screaming meltdown because she had lost about 6 sets of airpods and when I pointed out...
So first of all, stay OUT of a meltdown and do not get involved in fixing problems which are being expressed this way. Obviously if there is screaming, investigate if she is OK, not physically hurt/hurting anyone, there is no immediate emergency, but once you have established there is no emergency, disengage. If she is shouting directly AT YOU or demanding that you fix the problem, SIT ON YOUR URGE TO ANSWER THE QUESTION. If you're anything like me, I have an almost pathalogical inability to ignore a direct question, but sit on it. Even if you can SEE the headphones, do not say this. Your ONLY response to this kind of thing is to state, calmly, "I cannot help you when you are screaming at me. If you would like to talk calmly, I might be able to help." And then take whatever measures you need to hold the boundary of not engaging while she is so wound up, whether it means you stick your own headphones on and ignore her, or put a door between you or whatever.
...she might try and actually find them and still gave her a pair of my wired ones, she then continued to tell me how awful I was etc...
This is why. Because you could actually do everything "right" and solve the problem, but the problem is not that she has lost the headphones. The problem is that she is stuck in a heightened emotional state. She can't engage in useful things like trying to find her own headphones when she is dysregulated like this - this is why she's going after you, even though you want to be helpful!
Any engagement that you give towards the red herring of the lost headphones is oxygen. Any engagement that you give against the unpleasant behaviour is fuel. Her emotion is like a fire at those moments, and will consume all the fuel and oxygen available to her, but it will also burn out when there is none left, because it's just an emotion, and they don't last forever, even when they are explosive and all-consuming like this. The quickest way to help that happen is to starve the oxygen, ie, do not engage with the red herring problem (which is the lost headphones) and try not to add any fuel by reacting to the unpleasant behaviour. IME, reacting to the behaviour, although it's not great, is less of a problem than engaging with whatever the red herring is.
...even after I went and found her a pair.
I took the wired ones off her and said fine if you can’t be civil you can’t have them but I was called abusive because I took her earphones she needs to wind down
So what happened here is that you gave her fuel by reacting to the behaviour, and so she has now shifted tack because her emotion-fire has latched onto this new thing to be angry about instead. But again, whatever her emotion has latched onto which is the nearest thing to be angry about is a red herring. The problem is not that she doesn't have headphones, it's that she's gone into an emotional firestorm. I am guessing that if you tried to reason and explain that it was her own fault you took the headphones back, that would have just prolonged the argument, and you already know this, so what most likely stopped it in the end was you realising she was beyond reason and disengaging - at that point if she had nobody else to bother, it likely didn't last that much longer before fizzling out (even if she was then stewing in feeling that everyone hates her and is denying her the tools she needs to regulate etc).
This whole approach might feel cold or uncaring, but it is actually not, because you're not withdrawing your support/help, you're just postponing it, and most problems are not that urgent. It was a really really important thing I had to learn. It has basically been transformative. I was getting stuck in wanting to validate and hear the emotion/communication, even when the delivery wasn't perfect, because I had in my head that when a child or YP is in meltdown, they are not capable of talking/discussing calmly - and that's absolutely true!! They are not in the headspace to be able to do that. But there is also very little which is truly urgent enough that it is worth giving oxygen to the emotional outbursts. I think I thought that when a child/YP is in that kind of emotional state, they can't calm down without my help, but firstly, they will. Even if the meltdown goes on for an hour, it will eventually end. If nothing else, carrying on and screaming is exhausting and you physically could not keep it up. Secondly, engaging with the red herring which is the problem does not help them calm down anyway, because they will still have all this residual feeling that they want to vent at me. And I'm actually teaching them a really concerning message which is that if they want a solution, they had better scream and shout, or hit, and demand because that's one sometimes-successful method of getting it, because it is genuinely hard for them to think of or follow through on any solution when they are in an emotionally heightened state. But the message that I actually want to teach long term is that you can't solve a problem when you feel like this, the first step is to calm down. I struggled with this part because as you are probably aware, a child/YP in this kind of state won't hear that at all, and probably doesn't know how to calm down and may well believe that they can't. So if you are struggling with this or you feel that you do need to engage somehow, the thing to keep in mind is to engage only with the problem of the emotion being too high rather than engaging with the problem of the lost earphones, or whatever the red herring is. So, validation of the feeling without offering advice or solutions, sympathy without verbal input at all, (all the great stuff from the HTT books) modelling biomarkers of a calmer mental state such as deep/slow breathing, keeping your own voice low/slow and quiet, your movements slow etc. If it works for her, you can suggest things like breathing exercises or other ways to calm down but NOT as a solution to the red herring issue - e.g. if she is saying I need the headphones to listen to music etc - don't suggest speakers, or singing, or alternatives to listening to music. This can be tricky to find the line, which is why IME it's usually best just to not talk at all, and only offer nonverbal sympathy like holding out my arms for a hug, or to pretend to be very engaged in something else myself.
Also - don't get into the trap of she tones down her voice a little bit as an attempt to get you to engage, but you can see she's not really calm yet, or you start to discuss it and she instantly raises her hackles and dismisses the solution again - just say something like sorry love, I don't think we can talk about this yet, I do want to help, let's (have something to eat/have a break/get some space) first - and then don't take it personally when she flounces or insists you're refusing to help. You could obviously recognise her effort in calming herself down if that would be received OK, and sometimes when they have come down from the high level screaming/ranting/raging down to an irritable/petulant type place they can be more amenable to suggestions of things which might get them into a better space for discussion.
9/10 the "problem" disappears once they are calmer. 1/10 when they are calm they are actually willing to have a reasonable discussion and make an effort to try themselves. It does help.
I am late for school run, so I think the ending of this is a bit abrupt, but hopefully it makes sense.