I'm sorry that happened, but I hope you forgave her somehow...maybe she was confiding your story because she felt like she needed to help you too, and did a major slip up.
I had a friend that did this when we were young, everyone in school learned something about me that I really wish they hadn't learned, by the time it got back to me it had turned into a monster, totally different than the story I had shared with her.
Everyone forgot about it eventually, and so did I, but I was hurt too.
I understand that feeling.
Your friend probably would not do that again, and misses the friendship you once had. I can only assume because that's how I would feel if I were the person who slipped up.