I was going to say what Cherie said better.
Basically, you have a spoiled barrel horse. They are no fun to fix, and often can never be run again safely. I shouldn't even call her a barrel horse, since she was just hauled around the barrels without preparation. That can leave a horse hurting, confused, angry, and fearful. But still: a spoiled barrel horse.
I wouldn't necessarily hand over your horse to dressage trainers without your involvement. Maybe negotiate. See, if you decide to do it, they'll be putting buttons on your horse and you won't know how to ride her effectively. In fact, you can untune her as quickly as they tune her. So talk to them. Discuss dressage for your horse and lessons for you so you can ride her. Discuss western dressage. Is that an option?
Here is the thing: dressage teaches a horse that the rider is in control, and it gives a knowledgeable rider control over the horse's movements, to the point that you can have forward impetus without forward motion or ask for a right lead on a left circle and have the horse grant it and move in a balanced fashion. Having a solid dressage foundation can put you back into the barrel arena because the horse will understand self-carriage and obedience to the rider.