It may be taking her longer to process what had happened mentally versus emotionally. She is still holding onto what you've said. You may point out to her that she too had said some things and that you're not asking her to forget the incident, but not to allow it to control your future interactions.
There has to be willingness on her part to move past this. Remind her of the friendship you have had and that people make mistakes. Ask her what would it take for her to be able to move on.