How Do You Help

I find myself faced with a conundrum. A young woman I know of is being beaten by her boyfriend. She is not someone I am well acquainted with. I know very little about her except for her name. She is white, her boyfriend is black and this has caused her some problems with her family. The couple is essentially homeless except that my son has been letting them stay in his basement. Obviously I feel great compassion for this girl. No one should ever be brutalized in that way. On the other hand, any interference from me would not be welcome. She stays in the relationship in spite of the abuse. I understand staying because you feel have no way out. Lord knows I stayed married for fifteen long hard years for that reason. I just cannot have that kind of behavior going on around my young children. It is not acceptable. When does compassion for another person have to be set aside to protect your own family? This situation makes me feel helpless. I don't know how to help or even if I should try to help.