If I were you and somebody kept saying negative things to me. The next thing I said, before she could get a word out I'd say "do ya got a problem with that?" Or after she comment you could say "I see you took a happy pill today." I know this is really corny stuff. Like I said if it were me, I'd be dishing right back. "Treat others how you would like to be treated" right. So if someone's being nasty to me, I'll be nasty right back. You must be young, I can remember being like you. One day this middle aged guy said to me (I was 18 at the time), he said that one day I would get bitter and start biting back. Well wouldn't ya know I started biting back. I'll never forget that conversation. One day I just got tired of taking peoples crap. I think one day you'll get tired of it too and start standing up for yourself.

If you want to go with the e-mail just be like... Look (whats her face) somethings been bothering me. But first I want you to know that I consider you a good friend. But when you constantly complain about everything, it makes me feel uncomfortable and I don't enjoy our time together. Or something along those lines.

If she doesn't stop and you don't like being around her, then she's not your friend.