Should I change from snaffle to gag even though I want to do dressage?

Hold on a minute while I put on my Wishful Thinking hat.

PLOP.

There. Got it on and squared up, and I'm once again a certifiable Know-It-All.

I would train the other rider to have better hands. I would arrange for her to get lessons riding on the longe with no irons and no reins, having to do everything from seat and legs. Once she can ride from seat and legs she likely won't need anything other than a snaffle on most horses she rides.

I would also magically remove the objections to this sort of training, which include (1) that the rider probably believes she has good hands and (2) that she doesn't see how riding WITHOUT reins can improve hands--especially hands that were perfectly good already.

I would probably mention that cadets at the SRS spend ample time riding on the longe, and that it's not just something for beginning riders. I would magically dismiss objections such as, "That may be YOU but that's not ME. I don't need that."

I'm now removing my hat. Feel free to borrow it any time. Good luck.

gags are not permitted in any dressage ring. as said above....she needs lessons. try a fench link. has 3 pieces is still gentle enough if you make mistakes with your hands, but is accepted in the dressage ring. No copper is allowed eitherr. My ottb gets strong too. At my last lesson the instructor recommended a martingale and a gag. I am looking for a new instructor who has a stronger foundation riding green horses, preferably with a dressage background. I ride a hunter.

She is likely the reason he is strong in the mouth, don't put a gag in his mouth you'll risk him getting really bad

just because she has heavy hands does not mean that you can not teach the horse to be softer. but i like your backwards thinking.