Does any anyone else have to deal with a sister n law from hell?

Yikes! She sounds like a nightmare. I have dealt with a horrid sister in law, who ended up leaving my brother because she was having an affair. Surprise, surprise! She showed her true colors. That said, as horrid as she was, I was still always nice to her face. And so should you be to yours. Be the bigger person by doing the same. But, I also lessened how much time I saw her. So do the same too. That way it's much easier to be nice. I really stopped seeing my brother as much as I would have liked. But it made it much easier to be nice to my SIL that way.