frustrated

My mil has allowed her husband to physically and emotionally abuse her for over 30 years. To this day he still hits her and yells at her and she does nothing. He even pulled a gun to my husband's younger brother because he was defending her and she still didn't do anything. Wouldn't you call the cops or kick him out?!?! When my husband and his siblings were kids, their father treated them like shit and she never stood up for them. I hate being around that man because of the way he is. He's bipolar but refuses treatment and treats my mil like a servant but it's her that allows that. I used to feel bad for her until she told me that God hasn't told her to leave him yet. Honestly that's when I stopped caring. At this point I kind of resent her for allowing this man to cause so much damage to this family and to my husband and all because god hasn't given her the permission to file for divorce. When I met my husband he was practically broken and didn't know what it's like to have a father even though he has one. Sometimes I just want to tell her to just do us all a favor and get rid of that man because he's nothing but an abuser. Even the way he treats their 15 and 12 year old granddaughters leaves me speechless but to my mil it's nothing. Is it wrong that I resent her for all of this? I just feel like we all have to deal with that man and his hurtful ways just because she doesn't want to leave him.