Can I just say I'm really sorry you're in this position. I kinda understand, I've witnessed it with a family member in the same boat. The most important thing is that your husband isn't triggered by it nor you, the more you ignore her behaviour the better. The only way you can overcome it is if you two stand strong as a team. Every time she says something to him about you, his first response needs to be to protect you, and to let her know under no circumstances is she to tattle on you, he won't stand for it! That's what worked with my relatives, they had to be pie hot about it. I know it's difficult, but if you can find a way to move that would be the best option, then you don't need to deal with her at all. If it makes you feel any better, when she passes nobody will care, and there will be lots of light heartedness at the funeral, I know that's what I experienced!
You can always imagine that on your worst days, lol
If it makes you feel any better, she is probably like a bunch of mothers with sons are, nobody is good enough for their little boy! I don't know why some mother's are like that, probably insecure or needy, I dated a guy once who bought me a really nice gift, and his mother was very upset he did not buy her the same gift. Which would be totally inappropriate for a mother, in fact she was a nightmare all around. He never protected me from her, and after we started to not get along for other reasons I met someone else and moved on. We stayed friends and he started to date a real witch (just like his mother!) with a child & she begged me to take him back HAHA. No thanks! I never in a million years thought that woman could like me, but deep down your mother in law probably does, she just finds it hard to show it.
Anyway I digress, she's only doing it because she's bored, insecure, still thinks she has power over her son and she (so far) is getting away with it. That has to stop. her actions must not have any affect on you guys, at least not outwardly to her. If it causes any probs, do it in private don't let her see. Be a constantly unified, happy front!
No amount of talking to her will help. she will not listen. She'll just enjoy the attention and aggro she's causing!
Meanwhile, listen to abe hicks if you like it, or it appeals to you, I love them they're fab! Here's a good free channel I found and enjoy but there are loadsss more you can search for that topic too
https://www.youtube.com/channel/UC-YgmJ_fR_eBNeUG1W4gOKg/playlists?disable_polymer=1
There's even a playlist about Relationships, not sure if there's anything about that, but it all helps. I'd start to write lists of all the things she does that I like, hard to do but even if it's only one thing, it will help shift the energy.
I have a shocking relationship with my parents, they are 'difficult' at best. If I
don't stay focused on the positives with them, it flips into a hell hole in a short amount of time. If I stay on it, reading my lists once a day of all the things they've done for me, or that I appreciate about them, they turn into angels. It's bizarre, but it works!! Don't let her grind you down, you will win don't worry!!
I always believe the good guys come out on top xx