Talk to her about it. Be honest, but gentle, and see if she will listen to you that way. It may be that she doesn't realize that she's been treating you that way, or it could be that she is having a hard time with something like a decision, or it could be something else. Try to understand why it's happening before accusing though because no one likes to be accused very much.
Also: ask yourself (and ask the girl to ask herself) "IF you could leave the relationship knowing that there will be absolutely no negative consequences for anyone, would you leave the relationship?"
neither of you has to tell the other what your answer is, but it will help you look at your relationship without any emotional baggage/ties aka analytically.