I hate rude people with bad manners....
Can you start training at the new location and slowly move your customers to it a little over time?
This is a tough one, but if I were a volunteer and treated that way I don't think I'd be back.
Why do you suppose they put up with it?
I really think the volunteers just don't know any better. They treat her like a goddess of equine omniscience. I'm not incredibly experienced, and I'm not a horse trainer, but I know that beating a horse into submission is just flat out wrong. The volunteers don't know any different, and they think "Oh, I guess that's just what you have to do then" According to the way she talks about 'good riders' the rougher you are, the better rider you are. Especially if you can make the horse freak out and then calm it back down, you must be a great rider. They are proud that they 'get' to work with her, so they put up with anything. Plus, there aren't many other places to go.