I’m so sorry for what you are going through, hon. I can tell you first hand that you saying something probably would not have done anything. My first real love boyfriend was physically abusive. My sister found out and tried to get me to dump him. I cut ties with her. I truly believed when he said he was sorry. I truly believed when he said he wouldn’t do it again. Then I believed when he said it was my fault he hurt me and that I was such shit that no one else would love me. Everyone in my life tried to get me to leave him but I turned on them not him. It came to a head and I finally stopped believing his crap when he pulled my own gun( a gift from my dad) on my and held it cocked to my head. He didn’t pull the trigger but I could see how much he wanted to. So no, you couldn’t have saved her just by saying something about a slap. Only she could have saved her. Her parents are hurting and need to blame the world. I highly suggest therapy, it the only thing that saved me after my ordeal. I hope this helps you.