Before she confronts you about anything, she thinks it over in her head, and for some reason or another thinks that you are going to tell her no, then proceeds to find a way around you telling her no. As far as the reason she thinks that you are going to tell her no, I’m not sure. Maybe it’s because she IS going to do or did something that you disapprove of. Or maybe it’s because for some psychological reason she thinks that you will assume that she is going to do something that you disapprove of.
Have you confronted her about WHY she continuously does this?
Here is another question: Is she much younger than you? The reason I ask is because a lot of times (and I know from experience), girls will date older guys for one reason or another, but then they think of them as a fatherly figure…thus making them go behind the man’s back so that they can “be their own age” without the man disapproving as a father would.
I may be way off about this, but I hope I’ve helped a little.