I used to own a horse that was severely abused when he was younger, he was only 6 years old when I got him and hated every human being with a passion.
He would not get brushed was any brush without kicking, lashing out, and trying to bite me. It was almost like playing dodge ball trying not to get bitten.
I would try every method, being gentle and super slow, and talking to him, Ignoring the behaviours, or being very stern and giving him a "HEY" and a wack on the shoulder.
None of the above ever worked and he actually bit my mother on the head so badly that we had to go to the hospital, and we had to sell him because after months of trying to work through his severe aggressions towards humans he was just to dangerous.
If your mare wasn't abused she may have sensitive skin.