The day after your talk, follow up by asking her what she thinks about your discussion. Give her the opportunity to express her feelings and try not to jump on the bandwagon if she begins to express some doubt. As difficult as it is, try to remain supportive and listen to what she says. If your daughter does not think that the relationship is unhealthy, perhaps you can reach out to others for support and help in figuring out if this relationship is, in fact, unhealthy.
Whatever you do, do not push your daughter away! She needs your support now more than ever – and your constant love will be the only way she will realize that what is happening with her boyfriend is not healthy.
If your daughter has a rav with whom she is close, try to get him involved. Explain to him what you think is going on. Perhaps he would be willing to meet with your daughter and the boy she is dating, and help your daughter figure out whether this relationship is good for her. If she does not have a rav, a teacher from high school or seminary with whom she was close can possibly help you in this trying situation.
If all else fails, perhaps you can convince your daughter to see a professional with or without the boy. The professional should be able to glean some insight into their relationship. She can tell the boy (if she is really serious about him) that she wants to have a great marriage, and that many people attend pre-marital counseling in order to help them form a strong bond – and ultimately a great marriage. Through counseling she will hopefully be able to work through these issues and if this boy is indeed abusive, she will be able to recognize this fact.
Please do not give up, even if your daughter is pushing you away. Hatzlachah!