I'm so sorry for the situation you're in. Its completely wrong how your wife's mother treated her, I'm also sorry for the abused she endured.

Familys are complicated, even without abuse. Abuse just makes me things ten times harder. You're wife just had to do whats best for her, put number one first.

In my opinion, her sister saying that to her complete tramples her feelings and devalues them. No one deserves that. Perhaps try explaining to the sister how this makes your wife feel. Getting her to I mean, or you. However it would work.

I was abused by my older brother (not primarily, as well as others). My Mum found out when I got hospitalized. She saw me and held me and said she felt sick. But she also remained loyal to my brother. I understand how hard it must have been for her but it meant I couoldnt talk to her about anything. It was really hard times. I dont really want to go into it too much more as I dont think it will be helpful.

But yeah. My younger sister, wasnt even alive for some of this and had no involvement. I want it to stay that way.

I kinda realise this isnt helpful now.. I just thought it was gonna be relevant.. Now im not sure. Sorry.