High Energy Only At Shows

Horses do need to become show seasoned, but there is aright and wrong way to do it
First, if your horse is not very solid in her comfort zone, she sure is not going to be outside of it.
You a acclimatize your horse to working in different surroundings, before ever taking that horse to a show
There are many ways of doing this, like hauling to different arenas, , just riding around other horses BUT, also making sure you still expect her to listen to you, and focus on you.
You might just haul the horse to some shows at first, walking the hrose around, lunging the horse, and maybe showing in a few in hand classes, and just riding her in warm ups
When I took a young green horse to some of the horse;s first shows, i made s sure to get there early, and I would lunge the horse, then ride the hrose, before the show started, making sure the horse was listening, just like at home.
I then would tie the hrose up, either in a stall, if I had one, or back at the trailer, with food and water] During this time, I would have my own breakfast, and get my show clothes on. A few classes before mine, I would warm my hrose up again
Point is, right from the beginning,you have to make sure your horse understands that the same rules apply in the showring as outside of it, and that is more important then trying to place
Once a horse has gotten to the point yours has, where she is actually rearing,bucking, you have to , first rule out both physical and mental pain, and then take her to a schooling show, where you don't even worry about placing, but rather schooling your horse, while making sure you don't interfere with any other horse and rider
You won't fix as to how she is acting at a show, just riding at home. Right now, by having allowed her to buck and rear at shows, she thinks different rules apply, riding at home, versus at a show
It is only natural that a horse is not going to be as relaxed at a show, as at home, esp in the beginning, that the horse will sense your own tension, which will cause you to ride different then at home, also, esp if you are expecting her to act up, then add the usual show jitters that is just part of showing
But, you can learn to control your own tension, which will in turn , help your horse to relax, and you can make the show ring a pleasant place to be, but, at the moment, with your horse acting up at shows, tot eh degree she does, she needs someone to school her at shows, before you can ever even think about trying to compete

Well, does not matter if you are lunging or or riding her at a show, you must let her know that bucking and rearing is not accepted. You can't expect a horse to do their own thing, lunged, and then expect the horse to behave under saddle.
Forget as to how she goes at home, and focus on how she goes at a show, making her realize same rules apply
Is she ever stalled at home, as she must be at a show?
You might ride her the same amount of time, at home, as in a few classes at a show, but that time at home is in most cases, at one time.The horse then feels work is over, once that ride is-the horse does not measure the amount of time
Therefore, you need to spend some time at home, riding her, putting her back in a stall, then riding her again-same as at a show
If I only have a few classes at a show, I don't just leave my horse in stall, but will ride that horse out, around the grounds, even down a road, if that is possible
I might then just let the horse chill in the hitching ring, relaxing, and put the horse back in the stall and feeding him/her, versus having the horse think that each time he/she is in the hitching ring, the horse has to perform