How do you deal with bullies in the workplace? How would you handle this situation?

I work part time at a place while I go to school and finish my degree. I've never had friends because I was always made fun of Elementary thru high school. I'm a junior in college now. I'm smart, pretty....I'm just fat. I'm humble and I treat everyone as human beings and don't cuss or talk bad about anyone...that's just they type of person I am. At work the other day, I work with a lot of teenagers, they were making fun of me calling me fat and all that stuff. I got mad. The girl who I thought was my friend, laughed to and now she's mad at me because I'm mad that her and this boy she likes were talking about me. Now, because of her, everyone hates me, no one talks to me anymore, and they exclude me out of everything. I'm usually cheerful and happy, but now I barely ever want to be there. I still flawlessly do my job, I'm good at it, but they're driving me to quit. I've already talked to the head boss lady, she came to me first because she and the rest of the managers knew something was wrong with me, and she said she'd handle it. I know I can sue if need be. I know this girl is defaming me (slander and libel). I thought she was my friend, so I opened up to her and now she's treating me like garbage. I try to talk to her and even said sorry when I did NOTHING wrong and she blew me off. This other person, who is very angry at the situation is going to quit because he's on my side and they're treating him just as bad. How do you deal with people like this? I'm pretty sure I graduated high school already and now I'm back in it?? I want to quit, it's sooooo uncomfortable working there, but I'm in college, I NEED the money and I LOVE LOVE LOVE my job. I'm management material there...but I feel like I have no choice. How would you handle this situation? I need advice. I don't have money for a lawyer so is there anything else I can do? I HATE bullies and she needs to go.