Please ladies no judgement!!!!

Today My sister had contacted me through messenger and told me she needed to talk to me but she was afraid that i would tell my other sisters or my parents. Immediately I became very worried because she never starts our conversations like this.. she told me she loved her boyfriend but she knows she needs to leave him. At this point I could only think of two reasons she would say this ( he either got another woman pregnant again or he hit her again) our family absolutely hates this guy she has three children with him and he is an absolute piece of shit to her he's left her multiple times for other women he's cheated multiple times and has also gotten another woman pregnant. He's never really supported his children with her at all.. He's also has hit her on a few occasions. She still decides every time that she wants him no matter what and will not give another man a chance with her.. she always falls back for him. Well this time he finally got her and the children moved out of my parents house and she lives about two hours away with him.. she ends up FaceTiming me and has the camera facing the ceiling immediately i knew he had to of hit her again or something.. shes begging me not to tell a soul or she will never forgive me while shes telling me what happened. I guess he got mad because she got drunk with her new friends at there house and they stayed over until 2am. At this point I knew he definitely hit her and I'm begging her to show me her face when she finally did I broke down crying from pure horror and disgust that a man would lay his hands on her like this!! Her eyes were completely black and swollen shut 😭😭😭 I begged her to please leave him and to come home her babies don't need to see that!! She defended him and said they were drunk she hit him first because he was choking her and she couldn't get him off he didn't know he hit her that hard blah blah blah I asked her what did she tell the kids she said she told them she fell and hit her face on a table! I so badly want to tell my mom but I don't want her to hate me for it it took so much for her to come to me. What do i do?? Im so afraid for her and her children!! What advise can i give her thats not offensive? She seems to not want to talk about it and is acting like she didn't just show me her poor face!!