You own the horse, pay board, vet bills, essentially all the expenses of maintaining the horse, and on top of that you are paying a trainer to train the horse, generally interpreted as improving the horse.
Suppose non horse owning Suzie Q comes to you and says, honestly, “I don’t own a horse but I’d like to pay your trainer $50 to teach me, a rank beginner, on your horse. I can’t get on his case is he’s naughty, and I may yank him in the mouth, but any retraining, of course, is left to you. Oh, since he’s a 4 year old and I’m a beginner, if he spooks and dumps me, I may get injured, in which case I’ll sue you for a million dollars as owner of the horse. Since the trainer couldn’t get her lesson fee without “borrowing” your horse, this is an excellent arrangement for both the trainer and for me. It’s just you, the owner and person paying trainer who gets nothing and bears all the risks.”
If you had been asked in advance if this arrangement was OK with you, by either the student or trainer, would you have said yes?
What the trainer did was a form of dishonesty and theft. Even if a trainer is up front about it and asks if it is OK, often trainers will try to guilt the horse owner into being generous and “sharing” their horse with others. But it’s up to you as owner as to whether you want to share or not.
In this case she just went ahead and stole the use of your horse without asking permission, putting your horse at risk. She didn’t ask permission probably because understood that it’s a beneficial arrangement purely for her and the student, and detrimental to you.
I have been the victim owner of this type of behavior from several trainers. It is, indeed, a fairly common set of circumstances, and because it happens a lot, it may seem “normal”.
But the fact that it has become somewhat normalized does not make it OK. Your instinct is that you have been cheated, your horse put at risk, and your trust abused. Your instinct is exactly correct.
You wanted to give the trainer the benefit of the doubt, which is generous of you. Since this sort of thing happens a lot, possibly the trainer “thought you would be OK with it”. When you asked her about it, if she were an honest person who respected you as a client and horse owner, she would have fallen to her knees offering apologies for overstepping without clearing it with you in advance and swearing on a stack of bibles that in future no one other than she and assistant would be on your horse. Had she done that, you could provisionally go back to trusting her.
Once a trainer has clearly demonstrated dishonesty or lack of respect for me as a client, I’m gone. I don’t confront them to inform them of precisely why they’ve lost my trust and vent, and actually try to leave on pleasant or neutral terms. I say something along the lines of “You’re a great trainer, but I’ve decided you and I are not a good match as trainer/client and I’ll be leaving at the end of the month.” It’s likely that she’ll understand you’re leaving because she abused your trust, but you don’t owe her specifics beyond “This is no longer working out for me.”
If it were difficult for me to walk away because there were very, very few alternatives available, I would calmly inform her that you are very much not OK with her having anyone other than her or the assistant ride that horse and “clarify” (insist) that she agree to get advance permission before she puts anyone else on the horse. If she fires you for expecting to be respected as a client and treated honestly, pop a champagne cork at your good fortune.
You come back 3 Years + later to clarify?