If you have tried everything, then im sure she's just not the horse for ring work. If she loves trials and out in big open spaces, then spend most of your time there
I don't do western, im only english. So not sure what else to do.
Explain how she's getting bored, is she really slow and dopey, and then a different horse when she's in open spaces? That's my quarter horse is like.
When he was young, he was kept in a small area for a long time. (nothing like neglect or anything, but he grew up in a small area.)
So whenever he saw big open spaces, he would get soo excited! Just bursting with energy, he is still like it now.
Maybe just let your horse go for a nice canter around the ring to loosen up, and then try texas barrels, or something you would do out on the trails.
Have a go at bareback, vaulting on and off, have a tennis ball, and pick it off a big cone, then put it back on there.