The donkey must learn who is the boss and who is not. Right now, she is the boss at your house, and will continue to be until you convince her otherwise.... She wants to hurt you, hurt her back more until she understands the lesson.
If she decides to bite, I learned from a horse lady, that a sharp uppercut to her chin (she won't be able to see it coming) will sop the biting. This tactic won't make her head shy, because if done correctly she will not see your fist coming up under her chin. She will just know that every time she takes a bite, she gets whacked and it hurts.
Tough love!
