Im sorry for you ladies with the bad MIL relationships. It's gotta be tough. My MIL is much older and in a elderly care home. It's been unfortunate that with her mental state that her and I have never been able to build a relationship. I've heard only wonderful sweet stories about her.
However, I have a sister in law that sucks. I've been told that she said in reference to me, "None of Robert's other wives were good enough for him, what makes her think she'd be any different?" I don't care for her too much really.