You may know she deserves better but the question is does she know that she deserves better than what he is giving her? Depending on how long she has been putting up with him verbally abusing her, he may have her self esteem lower than it was when she got with him and therefore doesn't believe that she deserves any better. He may have knocked her so much that now she is starting to believe it. When a man that is suppose to love and care for you tells you or makes you feel like you are nothing after a while the woman starts to believe it and then feels like no other man would want them. Until she realizes her self worth and what she deserves she will continue to go back to him, she should have left him and never looked back but if he made promises that he would change she may be trying to give him the benefit of the doubt but that will only last so long and then she will be miserable again. You may have to put your feelings out there and tell her that you still love her and want her back and then give her time to think about everything that way she knows what you want and if she doesn't follow suite then I would suggest slowly making less contact because you want her to realize that this guy is no good for her but she has to do that on her own you cannot tell her that you think she deserves better she has to know she deserves better than he is giving her and then want to have someone in her life that respect and loves and cares for her.
Just make it from the heart, tell her that you have loved her since the two of you broke up and that you would stick out my life for her like you said in your first question to me. Telling someone you love them is never desperate the only way it would sound desperate is if you used alot of "Please come back to me", using alot of Please and begging will only turn her off so try to stay away from that just tell her how your time you had together meant to you. Mention all of the fun and romantic things you did and then ask her if you could ever have that again. Do not tell her you are desperate for her to come back if she thinks you are sitting there pining for her she will take longer to come back.