young horse suddenly stall shy @ show

Question
Hello.have just turned 5yr wellbred Arab trained by my daughter.been to local shows & 4-H. Horse exceptional/blue ribbn.3 month ago/new barn.No probs. Last 3-4wk/ went off feed, lost wt. [did this also, last barn in winter, but NOT so BAD]. At New barn, turnout @ nite, due to the heat.Went to Show this week & horse was insane when put in stall.It was a Closed stall/open to alley only.[In current barn,is open with bars]. If no other horses were there.
she was a MANIAC.She went BALLISTIC.  Totally OUT of character.Wanted to go over the door. Pawwed,bucked raised hell for 2 hour or more in the stall. We had closed the top door to contain her.NEVER happened before,[ in the last 2 years Showing there]. She was okay if there were other horses around, but when they left & she was alone,THIS TIME, she got psycho. So, it has to be her going out at nite with the others? Should we put her ALONE in the day..keep her IN at nite? We have our very first A- Show in 2 weeks & I just am at a loss how to handle this sudden upset.
You should know we just started ricebran oil a week ago to help her wt gain. Could that be making her hot? & add to the prob?

Answer
Hello,
As prey animals, horses have evolved into existence today by not leaving the herd and not going into caves. If your horses ancestors would have found themselves in a new situation, a new cave, without any other horses around and thought, "oh well, Im sure it is for the best". Your horse would not be alive today. Even if you have been to thousands of shows and it has never happened before, your horse is just being a horse. Here's the good news. The more you or your daughter can learn to be your horses leader, the more the horse will view you as her alpha and see you as a herd of two. Then when your daughter asks the horse to go into a cave (show stall) alone their relationship will already have the foundation there and the horse will say "okay, I trust you, you have always been a good leader." I would put the relationship with your horse ahead of any show you have lined up. If she goes in a stall and is freaking out she is scared. If a child was that afraid I would pick them up. If a horse is that afraid I would take them out and do some ground work until the horse felt the easiest thing to do was to stand quietly with me. Set it up so being quiet with you is the easiest thing for the horse to do. You could also start practicing at home standing next to her stall door in one spot (dont move your feet) and leading her in and out of the stall until she is completely mellow and slow with it. Then when you get to the show do the same thing until she can go in and out of the show stall with relaxed comfortable energy. Find a Natural Horseman in your area to help you if you feel you need extra help.
Let me know how your show works out!
Best Wishes