Man up. It's, more than likely, going to take a long time for her to feel comfortable doing this. And, when and if she does, it isn't because she's going to feel comfortable with a cock in her mouth it's going to be because she feels comfortable with you.
I understand your problem. My women didn't like oral at first either. She had her own reasons as well. It took a long time and a lot of trust and history with me but she got passed it and I would be willing to go as far as saying she actually likes doing it now.
What your going to have to realize is that there isn't a way to "get her over this" it's something that she'll have to work through herself, if she wants to. Even then I don't think it's something she would actively "work through". I think it's more something she simply no longer minds because she's grown to trust you and be close to you. But you better figure that kind of trust and relationship closeness takes a good deal of time to achieve.