I'm going to end one of my friendships.
Why are you going to end one of your friendships?
She doesn't treat me well and I've had enough of her behavior.
People and friendship dynamics can change.  It is okay to move on from a friendship.
I'm not sure how to tell her without us having a fight.
You should be clear and direct about your feelings. If you would be happier ending this friendship, than that's what you should do.