How old is this girl? If she's a Freshman or a Sophmore, then I'd understand why she pulls jokes on people...it's because she's immature. If she's younger than you, then don't worry about it. I admit that I joked around when I was that age because I thought it was fun, but when I think of it now, it was really immature. As kids get older, they start understanding things more so just don't let her get to you.

If someone jokes someone at my school, there's always someone that backs that person up making the person saying bad things look bad. Even the "popular" people will back you up because if you joke someone, nobody will take you seriously in anything unless you were just playing around(everyone will know when you're just kidding). It's really immature and she'll eventually grow out of it. If she won't leave you alone, then just tell her off.