Maybe leaving is the best thing. At least you know that you tried your best to save the friendship. It was her lost. If she come back in the future reminder her what she had said and make her be held accountable explain why the friendship ended and explain it was really her fault be resending that email and anything she had sent you that is a reminder that she is at fault. Then explain to her if she want to be in your life she has to make some changes or she can't be in your life. It was very difficult when I end my friendship with my ex best friend when I held her accountable for what her parent had done in person and on the phone to me and how she had treated me. In the end I had to do what felt right for me when I left the friendship there are days I wish I could done something more. I reached out again after it being awhile and realized she hasn't change and never will. I was left feeling really sad.