Perfect Prep supplement helps calm them and it's legal, my horse will get hacked in every ring he will be showing in the day before the show, then if he still has energy he gets lunged or hacked in the morning before my classes, I'd also recommend walking her around the show grounds to get her comfortable with the area and if she's still nervous have a friend walk their horse with you so your mate is more comfortable
schooling shows and trailering off property around other horses helps
I have to ride my horse in the morning before the show to stop him from doing that. It works really well he doesn't get nervous he's just very keen and runs so the ride calms him down
Take her to competitions not to compete, work her in the warm up ring all day on and off and try hauling to other barns or public arenas just to hang out and practice
Hi, part of her nerves come from the fact that she is in a new surrounding, so the more you take her out, the more she should get used to it. The problem when horses become nervous is that we also tense up and get a bit nervou,s which is a vicious circle as the horse thinks - why is my humam nervous, i should be nervous too and so on... so its's really important that you also keep calm, take deep breaths, if necessary say to yourself that this is nothing.
If you can lunge her before the competition, at first give her space to lossen up and let out any energy, then slowly start to bring her in control on your circle, with lots of transitions, trying to get her in tune with you, your voice, the ideia is that her focus is on you and not what is going on around her. Not an easy task, any day, and certainly much harder at competitions. Good luck!