Everyone who has posted has said about the same thing and I agree with them. You should definitely have control over when and if your horse is used and should receive compensation for it (I would say in the form of lower board). She really has absolutely no right to get angry about it, losing a free lesson horse or not. She lost that right the day that owners changed for the horse. It's her responsibility as a business owner to make arrangements to cover the loss of a lesson horse by either getting another horse, using another horse already there, or working out a detailed and mutually beneficial arrangement with you. It's extremely unprofessional the way SHE has gone about things. I'm thinking this sort of attitude is common with a lot of instructors, as mine has much the same view on things. I've had many issues at my barn with her using my horses without my permission for lessons, camps, and trail rides (I either come out to the barn at a time she's not expecting me and catch her or another boarder happens to mention something like "Oh, I saw Ruby out on a trail today", not realizing that wasn't supposed to be.). It's also commonly known in the barn that if she does use your horse, you're supposed to have money taken off board, but never once have I ever gotten that benefit. It's another sticky situation here, because this is the only barn and only instructor I've ever had (been here 11 years now) and she's somewhat a friend of the family. She constantly uses any horse in the barn she wants for lessons freely, even though she has over 10 horses of her own. Very frustrating, but it's hard at times to prove she's doing it and also I'm not really in a great financial situation at the moment so I don't want to say anything to her AGAIN and cause a rift when I can't really afford to switch barns right now. As soon as my situation improves though I'm giving her a detailed list of all things allowed and not allowed, along with some complaints, and if it causes me to have to switch barns then so be it. It's worth it to get rid of all of the stress. Constantly building up little resentments is good for no one, including the horses.