Breaking up with a "friend"?

[Munchkin03]

How does one go about ending a friendship?

Basically, I've been in the process of ending a friendship. This person considers me one of her best friends, but she's never been that good a friend or confidante to me--just someone to go out with once in a while. She is, as I'm understanding more and more, mentally unstable and self-medicates by doing stupid things like shooting up Vivarin (I kid you not). It's very rare that I don't see her on some sort of substance--a typical extremely destructive personality. She's always been jealous of my other female friends (the guys not so much), and especially my sorority sisters. She's sensitive--but not to the needs and subtleties of others. She's more touchy than sensitive, really. I don't like walking on eggshells around people, and I don't like the stupid drama she brings into my life because she has to be the center of attention all the time. Having her as an acquaintance has drained me, and has damaged my relationships with other, more loyal and deserving, friends. She doesn't take care of herself, and I wouldn't be surprised if she ended up dead somewhere.

So, it's become evident that I need to cut her out of my life. I have basically ignored all of her phone calls, IMs, text messages and emails for over a month now. She still does all four, usually with the lines "Where the f--k are you?!" Most people would take the hint after a week or two. She's not that subtle.

Has anyone else had experience with this--when you try to let someone off the hook easily and they just don't get it? I think she will lose it if I tell her how I really feel, plus we have mutual friends that I don't want to lose.