I bring it up and she flips out saying things like it never happened but as I'm accuing her she may as well do it.
It sounds like she's trying to justify her behaviour to herself by blaming you. She wants a reaction from you.
Rise above it and stay very, very calm. Take the moral high-ground. One day she'll realise what a mistake she's made by which time you may have moved on and she will try hard to get back with you.
