The easier a girl is to get into bed, the harder it is to get her out of bed
I find getting drunk and introducing her to your mate works wonders
tell her how you are trying to be something that your not, and your trying to impress her.
I had a stalker for 2 years I had even moved 80 miles away and she talked to my brothers and friends on msn asking what I was up to. I tried everything I told her how ugly she was, how I hate her, and the stupid little slut went to all the girls I was dating and said stuff, and generally was a jealous cockblocking whore, and would not leave me alone, and one night I introduced her to mike, (who "desprately needed some pussy") and didn't care who it was, so they slept together that night (lasted 5 minutes). and she kinda left me alone after that.
It's basically just letting someone else be the alpha-male, You need someone to take this girl away from you, so you look up to them and try and impress them and they become the alpha-male. ITS THE ONLY WAY. makes you feel stupid like a loser but their attraction goes down. I did it a couple of times. Give them a one-sided battle.
There are drawbacks on this as you have to put up with the "whats wrong are you jealous?" crap. and ridicule from people who know them and you.
BUT, at least you are rid of her for life

She will never try and come back to you either