thank you for the link. I think I had started to respond last year and then noticed it hadn't been active. Now I see it is alive again, so have given some advice.
I had contacted two lesson barns. The first I've decided against. The 2nd we exchanged voicemails and then the weather got crappy, first a week or two of deluges, and then 90 degrees with extremely high humidity. I may try the 2nd one again, once this heat wave breaks.
I've had time to analyze my last sit on Dahli. She started out not holding still to be mounted. Until now, she has stood stock still. So I regressed a little to how we started, with me actively asking her to stand still and just laying across the saddle. She stopped fussing and let me mount after that. She walked on without the balkiness she had shown in the spring and we did some simple walk-halt-walks. And then I could feel her starting to get a little fussy again. I got off before she could pull anything, and before I could fall apart from waves of fear.
What I realized is a bit of a conundrum. I need to keep her on a contact with the bit, so if she drops her front end to buck or lifts it to rear, I can immediately turn her head to the side to prevent it. But when I keep her on contact with the bit, then she is "ready to go" and waiting for something more than walk-halt-walk. But I don't feel ready to trust her at a trot until I feel her totally relaxed, which doesn't happen unless we are "walking out" on a long or free rein. Which I don't trust her not to take advantage of right now, since she seems to be testing limits every step of the way.