I'm not going to stay friends with a girl
Why not stay friends with her?
She posted a bad review about my book
Just because she does not like your book, does not mean you should stop being friends. That is petty of you to do that.
It was just a bad day and it was easy to break the friendship when my ego felt hurt.
Her being honest should not hurt your ego. You should appreciate the honesty of friends and not drop them because of it.