I'm sorry you're going through this and I know how you are feeling. My difficult child had a baby with her abuser. Shortly after the baby was born she left him. I did everything I could to support her during that time and helped mulitple times with police reports. When I found out she was back in contact with him I told her she could not stay in my house and continue to have contact with him. She packed up the baby and left late at night in the snow walking. I felt like I would die, it was so scary and painful. I had very little contact with her over the next 6 months while she was still with him. I babysat and I bought things for the baby, but I never gave her anything that he could benefit from. I was terrified the entire time that he would hurt them or kill them. It was a living nightmare. I really had to learn to focus on myself and what I could control. I joined a support group through our local domestic violence shelter and that was more helpful than anything else I did.
She is away from him now, and has been for more than a year, but I still worry sometimes. The breaking point for her was when she left him again and met him so he could see the baby and he snatched the baby and ran off. After that she was done. All the talking in the world from me didn't help. There has to be something within themselves that finally clicks, and sometimes it never does. Try your hardest to let her know when she's ready to get out you will support her fully and be there for her. That alone is something that really helps a woman in an abusive relationship- just to know when she gets the courage to leave she has somewhere to go. I know it's hard not to be judgemental, but I really just had to not talk about it with my daughter. It only caused fights and made her more determined to prove me wrong about the jerk.
Do something nice for yourself, keep yourself BUSY and try to stay focused on you. I know how hard it is. I'm sending positive energy your way and to your daughter that she will find it within herself to get out.