I think I just gave birth to a cow...
Yanking on a horses mouth does nothing, gets nothing done, and teaches nothings. I've never seen a real horse trainer, or a well trained rider, be hard on a horses mouth in order to teach it something, much less scream at it, because screaming cures all woes. That's just totally insane.
Now, a horse with a hard mouth may need a heavier hand, but there are ways to turn a hard mouth back into a soft one (usually). But a strong hand and yanking are two different things.
I would have dragged that lady off my horse, personally, but then, I have a not so nice temper.
I can't stand "trainers". They drive me crazy. Which is probably why I've been so wary of using trainers and some training methods. My friend had an experience with a trainer who would stand in the middle of the arena and crack a whip while she was riding her horse. Her mare (who was very spooky) ended up with a freakish fear of one part of the arena because that's where the whip would usually get her. To me, that's just dangerous.
And throwing rocks and balls at horses is different too. A rock could do some serious damage, so could a ball, but they don't have sharp edges, and they also have some give.
Ahhh. Some people just shouldn't be allowed to go anywhere near horses. I'm so sorry for all your guys' bad experiences.