I truly believe some horses don’t like going out on the trails.
I bought 3 Tbs off the track, gave them the same re-training.
One LOVED going out on the trails by herself or in company, was always ready to explore new trails.
One didn’t care one way or the other, was fine on trails.
Current one HATES the trails.
After lots of patient re-training over the years I can ride her on the trails fine, she is better with a buddy but might still jig on the way home even after a 2 hour ride, and if I want to take her alone, every year after she’s had some time “off the trails” for whatever reason, I have to “re-train” her to it.
This is what I do:
We go a ways down the trail and turn around BEFORE she thinks of balking/turning around herself.
Next time, we go a little further, same protocol.
And so forth.
This is what has worked with her. Even at 21 she still jigs at times on the trails, but nothing like she used to do in her early years when she was rearing, bucking in place, trying to bolt…to the point I had to get off and lead the little jiggy Fruitloop the whole way back since I was alone in the woods with no signal on my cell - better safe than sorry.
So I totally sympathize with you! However, I bought this horse for eventing, not trail riding (and she was just fine going out full blast with jumps on the way lol)
At this point in my life though, if I were you I would give it a few more months (at least through the Summer) and if she’s still not what you want at that point, sell her and find a more suitable horse.