(“The trainer had a short video made of her work.”)

I already know the answer to this situation, and you probably do too. But despite rational explanations, some things are experienced on a visceral level which we cannot control. A fellow instructor recounts this episode. She has my complete sympathy. Even if you have never tried to teach a lesson, I hope you can imagine the dynamic involved.
An OTTB—very green and only recently retired from the track—was sent for training. He had been with his novice owner long enough to become the alpha and learn to push her around. He had very little appreciation of accepting the aids (or much of anything).

The trainer began to work with him—first from the ground, things like teaching him not to run over her as she turned him out and to stand still while being mounted. Their first few rides were a test of will. After ten days and much hard work, the horse’s attitude had changed quite a bit. He had developed a better rhythm, a consistent stride, a reach into the hand over a round top line, and a bit of swing.
Pleased with all the progress, the trainer had a short video made of her work. She emailed it to the horse’s owner.

And was monumentally deflated when the only comment she got back was that she, the owner, had been working on the horse’s square halts too.

A trainer not invested in the work would simply let this roll off her back. The trainer’s satisfaction, anyway, should come from the change in the horse, whether the owner appreciates it or not, right? Or, you may point out, that it is also part of the trainer’s job to teach the rider to understand what she is supposed to appreciate.

But that does not make the lack of positive feedback any easier to swallow, nor does the realization that a rider who cannot detect anything this obvious may never really understand the process or the desired result.

Is there a happy ending here? Only time will tell. The trainer will get paid either way, of course, but many times a person needs more recompense than that.