Here is the thing about abusive relationships. Only the person in them can end them by learning to stand up for themselves. You can try to talk to the person and encourage them to leave their abuser by letting them know how you feel but in the end it has to ultimately be their decision. I understand it must be difficult for you because it is your daughter as a parent myself I would hate knowing one of my daughters was going through that but she is 19 and you have to leave it to her.

I grew up with a Father who physically and emotionally abused me and my sister when he was drunk and while I am not usually a violent person the best thing I did was knock him out when I was older.