If you want your horse used some in lessons (good exercise for him) then write up an agreement that shows what you are willing to do. For instance, "Trainer XXXX may use Old Blue on MWF for the 10 AM & 2 PM lessons. He is not available on TTh nor Sat, Sun. In exchange for his use as a lesson horse, board and lessons shall be reduced to, $XXXX. Effective, immediately and subject to revocation without notice, by the owner, XXXXXXXXXX.".
If she doesn't accept that, then I would remove him from the lesson program entirely and start looking for a new barn and new instructor, simply because a/ I wouldn't trust her to honor the no use policy if I wasn't looking and b/ I think it's going to get uncomfortable there if you pull him.
Good luck, I think she took advantage of your inexperience. Good trainer or no, you've just learned your first lesson in sharp dealings by horse folks. Sorry.
***ETA**** I just read where you like doing things by e-mail. That would be an excellent idea in this case, if you can. Just send her the e-mail and see how she jumps, that way you don't have to deal with a blow up face to face. I would NOT allow any revision to the schedule you lay out, it sounds like you need to take back control of your horse.
Last edited by Dreamcatcher Arabians; 04-02-2012 at 12:30 PM.