How do you fully let go of anger from someone who has hurt you?

I have been struggling with forgiving a friend that I had in my life for 17 years, we were practically sisters.  She moved to the state that I was living in and we each have changed in many ways over the years.  But for some reason she expected me to be the same exact person I was 17 years ago.  But she would never admit she had changed.  Last August, we had a fall out and she belittled me, criticized me, made fun of me and my friends, made fun of my relationship that I am in with my boyfriend and was just very ugly to me.  And then reminded me of all the things she did for me over our friendship and then told me that she felt she was used.  What she forgot to remember were all the things I did for her, I never judged her, her life wasn't perfect, she made mistakes, and I was always there to support her.  This really hurt me to the core because she was one of the few people I trusted.  What I wanted to do was to fight back and point out her short comings, but I never did, I never made fun of any of her decisions or her relationships.  I know I took the high road, but I felt totally defeated and it made me felt like I lost the fight.   Then after that a few weeks later, she e-mailed me to "apologize" it was a weak one, and then went from that to talking to me like we never had that fight.  I can never forget the harsh words she told me, I can never forget how she hurt me.  So I was so angry I never responded and I know that she knew I was very mad and just didn't want to deal with her at that point.

Now lately I think about her often, but I feel that she should contact me because she was just so ugly to me.  I saved the e-mail that she sent me with all of the horrible things she said to me so when I feel like this I read it and then it reminds me of how hurtful and ugly she can be and I never want to go through that again.  But then my heart aches for my best friend and I almost am in tears because I miss her so much. 

I have thought about e-mailing her but I'm scared of what reaction I may get.  I know that if we ever talk again, our friendship may never be the same.  But at the same time, I'm still angry that she would ever treat me that way.

How do I fully let go of this anger?  I have tried, but I just can't seem to do it.