Not an instructor but a vet I had an appointment with just didn’t show up and never called to say he was on an emergency or had some other reason. He did that twice and the third time, I left him a very angry v-mail telling him my time is just as important as his and this is the third time you haven’t shown up and from now on I’ll be taking my business elsewhere. He even called the barn and told the BO that he’d be out at such and such a time and they waited for him and he didn’t show up.
I started using another vet and he told me he was surprised Dr. No Show had any clients since that was a normal occurrence for him.
I’d start looking for a new barn to ride at if she’s continually cancelling lessons that (I assume) you’ve already paid for. This is just not okay.