Bite her back. I did once when my loan pony bite my back when I made him pick up his feet, he never bit me again. Didn't think about it just did it and it worked.
That is so funny! I did exactly the same thing when I was a kid. My pony used to bite every chance he got, it got to the stage I had to stand on something at least 3ft tall to get on him because he bit me when I tried to mount him - he picked me up by my back once, drew blood, I still have the scar (29 years later). One day I was so angry I bit him on the ear, I didn't think about it either just grabbed that ear and bit as hard as I could he never bit me again either!