If by chance she did cheat on you, and this is her way of trying to make things "equal", then she should just be honest and come out with it instead of being vague and secretive about it. That's just one scenario. If she's ever tried things like this with you before, then maybe it's a test. If I were you, I would confront her about this.
If you do truly care about her, then you wouldn't cheat on her and just be up front about it. If there's a chance that this is her saying she cheated and wants things to be equal (which is still wrong whether or not you decide to), then you need to confront her and see if she has. Just don't do it.