[HotDamnImAPhiMu]

Don't write her a letter.

The only thing more childish would be, well, writing her an e-mail.

Part of sorority life is learning to deal with people as you would in the real world.

You say your goal is to "rid your life of so-called friends." Um, why is this a process? That's like saying your goal this year is to break up with your boyfriend. Just..... stop hanging out with the girls you don't want to hang out with. THIS IS NOT DIFFICULT!

Seriously, though -- just stop hanging out with her. She'll get the picture. Giving her a letter with every little thing she's ever done outlined in it will a) make MORE problems, and b) make you look petty and small.

Write the letter if it makes you feel better, then burn it.