I’d love the share the benefit of my therapy from a similar MIL 😁
I do understand you’re not ready to hear this. The fact you want to send a thread to her- to righteously correct her bad behavior- demonstrates this in spades. But moving towards detachment is the only way.
her behaviour- and her examples, are a distraction. She can’t face up to her real feelings, so is using distraction by creating drama. It allows her to focus on the argument- being offended, recharging with accusations, waiting for the response, being mad, rather than deal with her feelings
her feelings are likely a deep rooted upset at her son having his own family, and one which runs differently to hers and sits outside of her span of control. This is deeply anxiety inducing. In emotionally unintelligent people, anxiety is managed by control (we all do this to some extent)
Responding is joining in the game, allowing her to distract. Allowing her to feel secure in her upset.
responding is a worse long term outcome for you.
there are ways to deal:
no contact- seems unlikely your DH would do the same so consider how much time will be spent with him nagging and guilt tripping you to see her (this is how he learnt to manage her)
low contact- detach and ignore. Move on. Send a message saying “sorry you feel tho way” and block her email address and phone number or send them to a junk folder.
divorce- consider whether DH is really worth it. Her influence is more powerful than yours because he learnt his behaviours in childhood and they are deeply embedded. This will cause ongoing stress throughout your lives and he is really unlikely to “choose” you (and consider, if he does, how strange that behaviour is- dumping one mother figure for another?)
If you divorce you could be free of this stress within the year. Forever.