Perhaps she’s not ready. If she’s a virgin, she might be waiting for marriage. She might be embarrassed. Either way, it sounds like she’s not ready to discuss it, and I’m willing to bet that bringing it up with a kind of forceful tone (if that’s what you’re doing at home) is not going to win her heart or remove her bra.
Besides, if she’s feeling that she’s not ready to talk about it, the sex probably won’t be that good. It’s better (imho) when both participants are hot, willing, and ready for it – not when one is doing it out of guilt or angst.
Here’s my advice. Perhaps she is embarrassed to talk out loud herself, but it’s time to bring it up anyway, and maybe she would be open to simply letting you talk while she listens. But I wouldn’t start with “It’s been two years and, baby, I got needs…”—I’d start with how much the relationship means to you, how you’ve grown to really love her (if that’s the truth) and how much you want to please her, and that while you’re willing to wait as long as she wants, perhaps you can do something to show her how much you love her… like rubbing her feet, or making her dinner, or… or…
You have to make her want it because she wants it, not because you want it. She has to be totally ready. It needs to be special. It shouldn’t be an ultimatum, it should be a treat.
If it’s been two years, there must be a big reason why. Two years is a long time to wait. Rather than taking a sledgehammer to that big reason, gently defuse it as if it were a ticking bomb. It takes a light and careful touch, but the results are so much more worth it. And if, after all that, she still doesn’t want to—back off. And stay backed off.
The best bet is to plant the suggestion and give it time to grow. I heard somewhere that one good way is to behave as if your junk got shot off in the war – until SHE is ready, and then let her know it was there all the time. :)