Why is she acting like this?

Basically, I got rejected by a girl, about a year ago. We were friends before this and she used to like me too, but I guess I waited too long. Anyway, at first, it was awkward but over time we had become much more comfortable around each other again and were "friends" again. Lately, things have been a bit strained, though. She recently told one of my (guy) friends that she thinks "I'm such a d**k". I mean I have made a couple jokes at her expense, but no different than how I tease any of my other female friends. She basically sways back and forth, one minute she is a b***h to me, the next friendly. The next day, she was talking to the same friend in class about how much of a jerk I am (she thought I couldn't hear her). As a result, I essentially told her to f**k off. Yet two days after the fact, she started talking with me again like nothing happened. Why so "hot and cold"?