Has she had any vascular or lymphatic weirdness in the hind end since issues with hock cellulitis? Odd filling or not filling when you expect?
I ask because I have weirdness like that in my young horse. She recently popped with a really fat jiggly hock, which made me think of your old threads about the hock cellulitis. She has some other weird filling things, too. So it’s a bit top of mind.
There are several vascular/lymphatic weirdness things in humans that can cause pain. They probably occur, to some extent, in horses. We don’t have the tools to diagnose in horses AFAIK.
Unfortunately, just because we don’t find what’s wrong doesn’t mean there isn’t anything. Yeah, someone could probably insist she not express the behavior you’re seeing in the canter. But shutting down communication doesn’t mean the problem is solved.