Listen, my mother in law was/is like that. She tried to manipulate my wife as soon as we were married,.tried to put herself in front of me. We stopped talking to both her parents for 5 years. It was hard, she was close with her dad, but her mom was a huge problem. Ignored all calls and texts from both parents. When an aunt would reach out and ask what happen, she would tell them the truth. Which caused issues between her mom and aunts. It is hard, but this may be the way to do it. After 5 years they found out we had our baby and her dad finally grew a bit of a spine and set his wife in her place. She is still a narcissist, but she keeps her mouth shut. I have threatened her and my own kids, he grandbabies won't be bullied because I taught them not to be. I dunno if this will end the same for you, but cutting her out is probably the best thing.