Is there maybe another lesson horse at the barn who is very calm and quiet, and will ignore her being uptight? My suggestion is to make it fun again, in a way that clicks with your daughter. I don't know what she is into, but maybe a trail course in the arena, walking over a bridge, turning in a small circle in a "box" made up of jump poles, opening and closing a fake gate, we used two standards with a piece of rope, and the rope is what we moved. We also had a mailbox that we opened and closed. Stuff like that with hidden rewards in the mailbox maybe. I am working on starting an Arabian mare, and first time on her, she spooked at a cat, and I jumped off her. Honestly I am very nervous now when I get on her, as she is a high strung horse, and because she always looks at everything, I tense up when I'm on her, and her being an extremely green horse, she gets upset about that which of course makes me even more tense. What one of the other girls at the barn does when she's leading my horse around while I'm on her, is talk about anything and everything just to get my mind off the horse and being nervous. Works pretty well for me. Anything you do will take a while to have an effect, but I'd see if she's open to possibly just walking around the arena playing around with obstacles, whether on her horse, or a lesson horse that she trusts, and give it a few weeks. Maybe have a trainer talk to her as well, let her know that she's not alone in being scared to work the horse again. If after a few weeks she still wants to give it up, then I would back off. Maybe lease the horse out for a bit, just in case she changes her mind, or she ends up realizing that she misses going out to the barn. At the very least, she can still go out and groom him, and spend some time on the ground with him. Sorry for the really long post lol. Hope it all works out.