His crazy-EX- girlfriend won't leave me alone?

I just started datin this guy, weve been together for a month. He recently (5 months ago) broke up with his long time g/f, who he found cheatin on him with multiple guys (including his roommate/best friend) She found out that him & I are datin and he came to see me(we live 3hrs apart) & while he was here, she went to his house, got my AIM s/n off his comp., & IMed me asking where he was. He called her & told her to leave me alone. This past weekend, she requests to be my friend,on myspace,I denied her of course.She emailed me askin, "Why did u deny me, i know u dont know me & i dont know u, but u really seem like someone worth gettin to know" I emailed her back tryin to be as polite as possible,"My friendship quota is fulfilled for the year,if a space becomes available,i'll contact u" She then responds with "that was the nicest decline,i see what he sees in u,i would still like to get to know u & i respect u" Why would she want to be friends with me?How can i get her to leave me alone?