You're doing the right thing.
Repeatedly tell her that she does not deserve to be manipulated and abused. Tell her that you cannot be GLAD that she is being manipulated and abused.
The biggest danger is that it is normalised. I escaped from an abusive relationship and I had a sense, at the time, that it was different for other people, that they could have a high bar and walk away from an abusive relationship but that for people like me 
it was different. That I could never demand respect and get it I guess.
I've since read that the best way to raise a woman's self esteem is to make her believe that she has control over her own life. This is achieved through self-efficacy so if there any examples you can recall where she has made her OWN decision and followed through on the necessary actions to get to that place, that is an example of self-efficacy. Also experiences such as zip lininng, abseiling and creating art (pottery, jewellery, music) they all naturally raise a woman's self-esteem.
A book called ''a woman in your own right'' by Anne Dickson really helped me. It's all about boundaries.
The fact that she is so upset that you don't ''support'' her relationship indicates that she is also tied up in needing your approval, as well as her boyfriends. The two can never overlap now you have seen his manipulative and abusive texts. So, as counter intuitive as it may feel tell her that you know she has to make her own decision, find her own voice, identify her own line in the sand.
Good luck