Just to play the devils advocate, how available are you for 3 lessons per week? Do the lessons have to be for instance on Fri, Sat, and Sun after 3pm?
On the other hand, do you know for sure that the training rides from her are actually happening? Is your mare getting more broke? I have seen several trainers in my area, say they are going to ride a horse so many times a week and the horse not get ridden at all, the horse being used in lessons with intermediate or advanced children (I’m talking 14 and younger, although they are good riders) and lessons being counted as training rides.
The way this was supposed to go is what I recommend for training anyway. I think you get the most bang for your buck. I never just send a horse for training any more. They always come back skinnier, or covered in rain rot, or not as broke as the impression I was given. If I am there to participate and watch the training, I know exactly how broke they are. I set it up as a lesson basically and if its rescheduled they aren’t touching my horse without me either.