cdn is right -- if there's no integrity, what do you have in a relationship? Nuthin'.
I also find it strange that she refuses to talk about it and tells me I'm holding it over her head if I bring it up.
Relationships are for growth! If one partner stonewalls the others' communication and won't engage on the important subjects that come up, she's not really being much of a partner, is she? You're left walking on eggshells, mystified and trying to figure out what's going on. Again, what kind of relationship is that? Not one that work for me. Does that work for you? You can't make her engage or communicate, but you can stand up for your standards in relationships, and that can mean letting her go so that you can find someone who is willing to strive for values you both have in common -- like integrity and communication.