Bella, Lawsa-mercy, Girl, you are one caring person!!
The only advice I really have to offer you is to not get "too" involved. As Guiness said, it's up to your friend. Its her life and she'll have to live with her decisions.
I CAN say, having been on both sides of the fence that the more you tell her what a pophead he is, 1) the more she's gonna either do her durnedest to find SOME redeeming quality in him and 2) the LESS she's going to confide in you when it comes to the relationship and/or listen to you, and 3) the less likely that she'll come to you for help when she "needs" it.
I introduced one of my best friends to my ex's dorm-mate several years ago. They hit if off and soon became an "item." Shortly thereafter, I began to notice that she wore more make-up, wore tighter clothes, began (ab)using alcohol AND began sporting bruises. She had the most beautiful long, chestnut hair -- the envy of us ALL -- and it was her pride and joy. She cut it ALL off and bleached it blonde because HE told her to.
You get the picture.
I was young, I was stupid, I was brasher than anything you can imagine. I also had no tolerance (like anyone does, of course) for bullying and abusing others -- much less MY friends. So I did my best to convince her to leave his sorry butt. She just worked that much harder to "make it work." She also began avoiding me, much to HIS delight, like the plague. Soon, I went from seeing her daily (we grew up on the same street) to seeing her literally twice a year.
I did get invited to their wedding, though (don't know why), about 3 years later. She was absolutely beautiful .... broken arm in a sling and all. And the makeup job was perfect -- you could barely see her black eye.
To this day I feel guilty about it. I keep thinking that perhaps if I had backed off, she might have seen it herself what a b@stard he was. But I really think that my immediately telling her how awful he was, kept her from coming to that conclusion.
Her story DOES end happily, though (as best it could, rather). The first time he hit their toddler, she was able to leave him. By that time, her entire family had pretty much abandoned her, so she spent time in a women's shelter, after which she got a low-paying job, went back to school and is now a vet (her BIG dream before HIM), remarried with two more kids and HAPPY.
So I took the moral of the story to pretty much be that if you tell her he's bad news, and she doesn't listen, it's going to take more for her to realize it than just your saying so. She's going to have to find it out on her own. But that's not the end of the world (though it DOES feel like it). She can make it. She can still have a happy ending. And it will be of HER own making. Just be there, as long as you can, to offer her a comforting shoulder to cry on, a couch to crash on when it gets really bad, and advice when SHE ASKS for it.
At least, that's the lesson I learned from my experience with a friend going through the same thing. :/