Thanks for the YT upload!
She’s cute as a button! She definitely has a lot of draft characteristics.
The fact that she has issues outside of just being ridden tell me whatever’s going on isn’t just about being behind your leg/not being forward. A lazy horse doesn’t carry that to the farrier and picking up a hind leg.
When you had the saddle evaluate, what exactly was done?
When she started this behavior, did it come at or a bit after a point where you were starting to ask for more work? Was she kicking out early in the rides, or later into them?
Her age at which she started to exhibit this behavior is fairly typical for the onset of EPSM symptoms, at least from what I’ve gleaned. I’m still glad you’re sending (or sent) hair off.
I noticed in the video that at some point she was much more relaxed and willing, though even then still very lazy. Is that as good as she gets? Has she been better? I don’t know if you were just content to leave her like that since she wasn’t fussing or (and since I don’t know you or your ability, I don’t know what you know or don’t know, so no offense meant ) if you feel that’s her "forward and happy " mode.
In other words, how does her best movement in the video compare to this
After the injection had time to work I got on and gave her a test ride. It was obvious to me, and those watching, that her trot had improved. She was moving forward willingly and was stepping under with her hind legs.