hi, 23475.
The reason it is difficult to forgive is because you have it bottled up inside you, and if you continue the friendship without addressing how it hurt you (especially if her behaviour continues) you may always carry a grudge. I agree with BlueRose. You need to talk to your friend about it. I read a book a long time ago that discussed conflicts and how it is scary for people to confront others. What I took away from that book was a new paradigm shift. The book explained that confronting someone, especially someone that means a lot to you, is the most loving thing one can do. It means that you value the relationship and the person enough that you want to make it work.
There are no guarantees to the outcome. I just personally think that if you approach her (I know this may be very difficult, especially if you have never confronted anyone before) with both grace and truth about how you are feeling then whatever happens, you will find freedom..
take care