Not married, but I also avoid my SO's mother. Something happened recently where I dont see the point of even trying to maintain the relationship, to listen to her stories etc.

I say hello and am courteous on the rare occasion that I do see them, but also dont engage. Whereas before I'd ask questions or continue the conversation. Now it is grey rock and BIFF.

I'm not concerned with her reaction to this. She should know she fucked up, she knows I know she fucked up, so until there is an apology (there wont be) my withdrawal will establish a precedent that she cannot fuck with me- she doesnt get that access!

Do you care of MIL knows you dont like her? I would say, "I will not talk about a person behind their back" and walk away when she tries to conduct the gossip train. She has excuses for all her bad behaviors, but you can demonstrate that you see them for what they are, and choose not be around it.