i think your doing the right thing when you told her to call the police and not a family member.
i was a part of a family members drama every time they got into a abusive relationship, and i always was there for them lending money, a place to stay, and an ear to listen. it stressed me out so bad, and the friends i talked to i had to pull away because that person decide to stay in these type of relationships it was nothing i could do.
she is an adult and cant keep crawling back to mom when she's in trouble.
your teaching her tough love!