Well the obvious signs are easy. Bruises and unexplained scars and marks on her body. But when you see the two together is she afraid to disagree with her partner? Does she seem to be very submissive to him? You instinct and intuition as a mother/father should be enough for you to confront her about it.
The abuser tends to isolate her from family, friends, she seems scared of him. She has bruises she makes excuses for his behavior. She lies about marks, why no contact.
