To rip MIL a new one?

Op, it's sad mil has done this I wonder if she doesn't understand and feels sorry for your mum.

Unfortunately I can't see any way around this other than immediately cutting mil off no phone calls or contact until she gets the message.
She can have a relationship with her son and his bride to be or your mum?

End of no negotiations just do it and mean it.

If mil kicks off very calm, I'm sorry but we told you not too and instead of respecting our wishes you are doing the opposite so it looks like you have made a choice.

I'd say this was extremely serious and unfortunately unless mil gets this message loud and clear it's immediately cutting contact.

Otherwise what's her motivation to listen??

Looking ahead I would be worried that, if the relationship between DM and MIL continues, MIL will facilitate DM seeing any DC behind the OP’s back which, presumably, OP would hate. Therefore I think NC may be the best option.

It's more than just unfortunate wording.

"You are alienating me by consistently going against my wishes, and hurting me very much by having this relationship with my mother. It causes me great heartache and distress that you care so little for me that you have no qualms about causing me so much pain.
I don't feel like I want to see you as I know you'll continue to go against my express wishes, and your actions will affect our relationship for ever. You know that this is hurting me, and still you do it. It's unkind."

@Someadvice those that have never experienced toxic familial relationships and associated trauma often struggle to comprehend the severity, impact and reality of what you lived through. It’s so alien to them and maybe your mum presents as so ‘normal’ that it makes it seem implausible to MIL that what you experienced was really all that bad.

It may be that your MIL really is that oblivious, it may be that she is being cruel either way it doesn’t matter as the outcome is the same regardless of her intent. Even if it is a lack of understanding her bullish attitude and thought process of ‘I’m right’ makes what she is doing ultimately cruel.

She is hurting you and despite being told multiple times, is refusing to do anything to prevent you further harm. She has been warned, time to block on social media and cut off all contact. Show her actions have consequences, she clearly isn’t going to understand any other way.

Edited to add:: I also agree with other posters that she needs to know very clearly why you have issues with your mother, she may be under some illusion she can fix this as she likes to interfere. If she really does know the reason for low contact then there’s no excuse for what she’s doing.

Exactly this

Your MiL is either a stone cold idiot or she is doing this maliciously. Either way, she's not a safe person to share any personal info with.

As a stop gap until you can consider going NC with your mum, could you get a new SIM or dumb phone with a number only she has? Something that would keep her nasty messages away from the rest of your life and in a place where you can choose to read them when you need/want to

This. Nothing will help but going super low to NC

1. Ime it is totally normal for the parents (mothers) of a married couple to forge their own independent relationship/friendship and for that to include discussing the couple/any grandchildren as well as other things. This could well include meeting up for a day out together, etc.

2. In this case if your MIL has been told specifically about issues in very explicit, non-euphemistic terms (child protection order etc) and the trouble it would cause you to share information in this way, then she is still being unreasonable.
   She may (due to point 1) believe that you are BU to try to prevent her having that relationship of her own and that you two don't get to control who she can be friends with, but in this case if it causes harm to you (which you must demonstrate to her by explaining about email comeback etc so she understands) then she has to choose one or the other (and it should be you and her son that she picks!).
   Be aware that if you cut her off and she carries on seeing your mum then she will only be hearing her side of the story and might become concerned for her own son - feeling that you are an evil cutter-off of perfectly nice mothers and have now led her son astray and forced him to cut her off too.

This is probably good advice even if difficult to take.

If your MIL is rather thick, prone to interfering in her own children's lives, and a bit bored, she might take it upon herself to bring the family together. She'll be imagining some sort of perfect Disney Christmassy ending.

Some people just totally lack the ability to read between the lines. She's probably thinking "Oh! Sometimes my children get cross with me!" (which sounds likely ...) and imagining the same kind of scenario, not an abusive one. I know it goes against the grain to tell this insensitive woman such deep personal details, but if you marry her son she'll probably find out eventually anyway.

I wonder if MIL sees it as a back handed way to get at you? She says ostensibly nice things to your mother about you, knowing that your mum will attack you over them. Then MIL gets to act butter wouldn't melt because she can't possibly be at fault because she said nice things.

Stop seeing MIL all together. She has been told not to contact your mum and far from stopping she is escalating. It's not that she doesn't understand the request but that she is ignoring it. You can't make her stop contacting your mum but you don't have to see her or tell her anything about your life.

Don't feel bad about the dysfunctional dynamics in both yours and your partners families, some families are like that and the best thing you can do is break the pattern by not engaging.

I wonder why MIL does this. Have you ever asked her?

It sounds like she had minimal information I. Your life. I would leave her to your mum. Let them do whatever they like and keep them both at arms length. Does share anything with MIL that you don't want getting back to your mother.

MIL has really crossed a line. I'd be concerned as to what she's hoping to achieve by being so interfering.

As she's been asked multiple times not to get involved with your mother, let her know that you won't be present where your mother is, which includes Christmas gatherings. If she continues to interfere, have limited contact with her. What else can you do when she's so determined?

MIL genuinely comes across as so oblivious to everything and I’m not sure if it’s all an act to get away with it or she really is like that.

If you have clearly explained to her that your mother behaves like this in response to positive messages, any adult of basic intelligence should be able to understand why she needs to stop sending messages.

If she is continuing to do so despite having had this explained to her, there is an element of either vindictiveness or saviour-complex power-gaming involved.

I would cut her off and go totally nc. She is stirring up trouble to get at you, as there is no other explanation for her speaking to a woman who has nothing to do with her.
tell DP he can do what he likes, but you are not visiting her and you want nothing shared with her about you ever again!

Set boundaries with MiL that both you and your DP (soon to be DH) can manage easily.

First off, restrict her access to your social media posts. You can post what you like but she is blocked/heavily restricted on what she can see.
Next, don't reward behaviour like her recent 'clever' arrangement with you visiting. That is an immediate line in the sand and you stay put.

She will stamp her feet and throw a hissy fit because you're no longer playing ball here but if you repeat the same message but this time refuse to engage with her when she pulls stunts like this, then she'll eventually learn. She may even recruit other relatives and relations to try to bring you back in line. Refuse to engage with any of them. A simple "If this is about MiL/Mum, I'd rather we not muddy the waters between us discussing it. I'm dealing with her separately on this. What can I do for you though?" and diffuse the situation by not engaging with them about this issue.

I'd even go so far as to say to her that her invite to your wedding hangs in the balance.

The next thing I would do is put her on an information diet - only share information with her that you wouldn't mind having sky written. If she shares that, then there is no harm.

It all starts with you and your DP/DH and how you manage things from this point onwards.

Have a look on here and on Reddit for the analogy about not rocking the boat because I think it fits this scenario perfectly.

You and your Dp put boundaries down so she is going out of her way to spite you by making trouble for you. She lives by her rules AND nobody tells her what she can and can’t do!
Cut contact immediately, block her and your mum on all social media and phone, if Dp wants to go, that’s his decision but he will have to make sure nothing gets back to her.

Where does mil get her information from about your life? She doesn’t need to know anything except what you choose to tell her.
Make sure all your SM is licked down so she can’t access.And go quiet on your wedding as it concerns no one else at all. If asked anything you and DP should be vague.

We are due to visit her for our annual Xmas visit in a few days and I want to rip her head off.

None of you go on this annual visit this year. Your DP has to support you in this otherwise it won’t work. She has to start missing out to realise you are all deadly serious. Ripping her one won’t work because she likes the drama. DP can go on his own but I’d take a dim view of him not supporting you.

It sounds like she actively going out of her way to make friend with your dm as revenge for you stealing her ds and then being low contact.

What a vindictive, nasty cow. If this were my dh and his dm acted the same he would've ripped her a new one himself. How dare she.

If you go to the Christmas meet-up, you might find that - surprise! - you mother is there too. Sounds like MIL would thing it a good idea to bring you both together.

Don't go.

My sympathies.
Your MIL.is out of order. She knows the relationship is strained, she's been asked repeatedly to butt out.
Cancel attending the event.

I have a struggling relationship with my mother (used to physically attack when I was younger, very critical narc tendencies etc.). My MIL used to invite my mother and father round for dinner parties (DP and I didn't go as don't live near them). I hated it. I couldn't explain why but it enraged me.

Cut all contact, she's insane.