She's So Mean To Me!

I have a problem. This girl in my class is always so mean to me! She's like super best friends with this guy and they always tell eachother everything. Well, one time this other person overheard them talking about me. This person said that the girl called me a gossiper, self-centered, and a liar. That really hurt my feelings because I don't recall doing anything mean or rude to this girl. From then on, things went downhill. She told me she didn't like me to my face and she treats me like dirt and randomly gives me dirty looks. Also, just today another incident occurred. I don't remember how this came up, but she called me a "goody two shoes." I thought goody two shoes meant that you always played by the rules, so then I said "No, (my friend's name) is kind of a goody two shoes." Then she's like "No, she's not you are." And then she called over her BFF (the dude she tells absolutely everything to) and she asked him if he thought I was a goody two shoes and that I think my friend (also his girlfriend) is a goody two shoes. Then he said, "Wait, what's a goody two shoes?" Then she said, "Someone who always sucks up to people." Then he said, "Oh, yeah (my name) is definitely one but (my friend's name) isn't." Oh, and may I remind you that this was all said right in front of me as if I wasn't there. Also, she does similar things to my best friend. She's very mean and it's far beyond a joke. I'm really tired of it and I need some advice on her. Thank you everyone:)

So, I used to find myself into similar positions. I see two ways to answer this.

Long term:
Really, the only way to cut this at the root--you know, people pressing your buttons like this--is to not have buttons that people can press. A way to think about this is a girl you don't even like so much has a negative opinion about you. If there's something valid in what she says, then examine yourself and make changes to make yourself a better you. If she's wrong, who gives a flip. Know yourself, and be confident in your good qualities. If you get upset every time someone says something about you that isn't true then... well let's just say if I had a nickel every time that happened to me, I could retire today!

Short term:
Stay away from her. Don't interact with her. Don't give her ammunition. Just ignore her. When she sees that her taunting has no effect on you, she'll likely lose interest.