I, too, have a toxic SIL. My husband and I have been married for nearly 35 years, raised a beautiful family together, but his sister acts like he and I are a couple of silly kids. My husband's parents were very loving toward me- not so his awful sister. My best sense tells me that for whatever reasons, she feels threatened by me. And it's hurtful because my husband clearly walks a line (or sits on a fence) with his sister and I. He will absolutely not really defend me to her, tell her to just plain knock off her odd behavior.

It's really tough to have crummy in-laws. All I can think of doing is avoiding her as much as possible, and taking the high road- for me, when I have to see the woman I'm polite, but certainly not warm.

Nice that you had a three-year break from your SIL. Hopefully she'll sort of fade away again.

Btw- I would say that keeping open communication about this issue with your wife is of utmost importance to your relationship. I mean, really talk with your wife- and really listen to her. Best of luck to you!