Hi there 9ofpentangles sorry you are having a torturous time atm which sounds hellish for you. Just like some adults, some teens are finding lockdown harder then others and are taking out all their frustration on those they love the best. And yes, I totally agree about avoiding the bits of Mumsnet where compliant teens are cooking pancakes for their wee siblings, having done 45 mins of mindfulness meditation in the garden , before settling happily down to their ancient history study followed by flute practice. Please remember that (a) half of what you read is not entirely true or it is edited to gloss over the difficult bits (b) all teens are different and those that cope well with lockdown, may not cope well in a different situation such as moving away and are storing up their melt-downs for the future 
(c) their brains aren't fully formed yet until around 24 yrs of age, and some are just unable, biologically speaking, to think beyond themselves yet.
Maybe it's a protective effect, a bit like toddlers whose eating habits change once they are able to roam a bit further? Maybe teens can only think of themselves at a time when often (developmentally speaking) they are leaving the nest, because it's a risky time, and they need to keep themselves safe? An evolutionary behavioural sort of thing? Who knows?
It's really frustrating and disappointing though when you are relying on them, now they are older to step up a bit and "help" I a difficult situation, not make it worse. I remember feeling really really upset when I was in hospital for an op at the beginning of last year and was hoping my teen would help a bit at home, make things easier for her dad, cook a few meals after I had come home maybe. And generally she was just dreadful; even worse then normal. She had been well prepped about it. And as everything unfolded it was explained to her that her behaviour was unacceptable several times and it was explained why , and although I think she understood on an intellectual level she couldn't, or wouldn't, translate this in to action. Thinking about it still upsets me a year on tbh.
Is there anyone else in the extended family your dd could go to for a bit? It sounds like you could do with a break. And I see this morning that moving in with someone else is allowed under the UK guidelines if there is a lot of tension in the air. Even if it wouldn't be her first choice to stay with an aunt or whatever, it might help her appreciate what she has at home a bit more?
Hang in there, this situation will evolve and change, and she will mature and be able to handle things much better. Not until she has thrashed about on the end of the rope a bit though! One day at a time and all of that 
. And feel free to vent on here any time.
Aramox that's genuinely great to hear about a teen for whom lockdown has lifted some school related pressures! I imagine your ds is not alone in that. Great to be able to have a legitimised break from all the academic pressures!
@Andi2020 how are you and your girls doing? Sorry about the emboldening failure further down thread!
Things are much the same here. Lots of uncertainty over end of year exams. And ticking along generally ok until dd has an almighty meltdown which is pretty horrible and generally lasts two days - and results in 24 hrs of silent sulking all round - then it's back to business as usual ... . You'd think I'd be able to shrug it off by now, but it still gets to me every time ... .
Waves to all PoTs 👋