If she truly loves you, explain to her what is going on. Take her to a good place to eat and spend a whole day with her doing the things she like, even things that you wouldn't do otherwise, like go to a play or whatever girls are into these days. (I once saw a three hour old romantic drama with my ex girlfriend. I think at one point I fell asleep, lol) She will understand, if she doesn't then maybe she is not meant to be with you. We are all human and we all forget things, if that is not true ask her if she can remember everything.