If the friendship is truly over and you're 100% finished...
Just ignore her the best you can. Like the other poster said, don't respond to any of her e-mails, voice mails, etc.
By responding to her, you give her attention. It doesn't matter that it may be negative attention, it is attention and you will only continue to give her the audience she seeks.
I'm going to guess that every time you try to tell her that you're not interested in continuing the friendship, she tries to tell you her side of the story blah, blah, blah. Ignore her and don't even give her the opportunity.
They say the squeaky wheel gets the grease, but if no one's standing around holding the can of oil....