Dear ntt91:
I re-read your original post as well as your reply above. I think that one heartfelt, sincere apology would have been enough as far as what you should do in regard to her. I think that having a friendship with her as things are is not a good idea. I think you should let her be and NOT apologize again.

As to your ruminations, obsession and anxiety- it seems to me that what FUELS it is deeper and older than the experience with the friend. The feeling of being a bad person, of hurting another or others and that being an unforgivable thing- WHEN did it start? When was the last time you felt that way, in regard to whom? A parent? Looking forward to read more…
anita