I have been having some issues with my mare. I need to find a different bit for her. I have tried her in a French long d ring/ full cheek, a regular d ring, a Waterford, a happy mouth, a Mullen mouth and a kimberwick. My issue is, she is getting waaayyyyy to fast and heavy in those and she is KILLING my arms and shoulders and core trying to hold her in. We have been focusing on slow work and she is GREAT at the wall and trot but the minute we canter she is a freight train. It isn't that she CANT collect and balance she just doesn't want to. She throws her head up and fights the but and leans on it and runs through it. I can hold her in but a lot of the time by the end lf the ride, arms and shoulders are shaking and my stomach cramping from trying to half halt her and check her. I am not usually one to just throw a bigger but at a problem, but I legit cant hold her in some days. She hates poll pressure so those kinda of bits are out. Any ideas??