What should a mother do when her Adult daughter is about to make the biggest mistake of her life?

My daughter is 25 years old and has kids of her own. She has been married twice. The first time lasted for about a year and from what she says was pure Hell. She admitted to me later that he used to beat her. The second one she has been with for about 6 years and been married to him for 5 and I believe she's about to go back to the first one. The kids are confused and I feel defenseless, I know she's an adult and has the right to live her life as she sees fit, but the kids are suffering because of the confusion and I know that she will eventually suffer too. He has just gotten out of prison(which he was in for 3 years) for about a year and was in there for his involvement with drugs. She hasn't seen him in 6 years, how can she possibly think about going back to him. Myself and my family has spent alot of money helping her get away from him the first time, and I just don't know how she could do this to her kids and hurt me this way, when I have been her biggest supporter:(