I once had a gelding that was somewhat like your mare. Not to that extreme, but he was bad. It sounds crazy, but like several members have said - BITE HER BACK. Legit. It works. Kind of like the idea that if a dog is being aggressive towards you, you bite it on the ear. Establish your dominance. Never go into her box expecting her to be bad. She'll know that you are afraid or nervous, and she will use that against you. She thinks she's on top.
Of course, be sure you rule out being in pain as a factor before you do anything else.
One man's wrong lead is another man's counter canter.
"Adjust Your Pleasure"
2006 Medicine Hat Paint Gelding