My mare was rode in a tom thumb before I bought her. She was suposedly ear shy from a ear mite problem. So I brought her home. Got her trust to handle her ears, taught her to lower her head, and started her in a D-ring snaffle. It all got better. Her previous owner rode very heavy handed, always in contact with her mouth, used a tie down to keep her from tossing her head. Needless to say she was very bracy with the snaffle. So I went back to the harsh bit, to gradually back off while still getting her to give. 2 rides latter she broke her lead rope when she saw me coming with the headstall !! All the problems come back in a violent outburst. The tom thumb went in the garbage can. It took a while to get her trust back, then teach her to give to much lighter cues from the snaffle. Bottom line is take the time to train her. She now rides on a loose rein with no head tossing, no tie down, and stands unhaltered be tacked. I bet you have the same problem. She is scared of the harsh bit hurting her mouth. Teach her to give to easy light pressure without pain. It will be a slow process to undo the the preception she asociates with bridling and pain.