Young horse mis-behaving.

Hello Everyone, I need a bit of advice. About 4 months ago I bought a youngster, she just turned 4 on May 1st. Basically her background is that she had been sitting out in the pasture most of her 3 year old year as her previous owner sadly passed away. When I bought her she had TERRIBLE ground manners, very pushy, rearing and pawing in the cross ties ect. Under saddle she would try to run me into walls and the round pen.

I've been working with her a ton and she has done a complete turn around..she stands like an angel, I can lead her without a chain over her nose and walks perfectly silent beside me..very nice and easy going now under saddle..but here is where the problem comes in..

My new barn (where I bought her from) does drill team, and I have never done anything like it before, and thought it would be a blast. I quickly found out she FREAKS out around other horses...I always go out to the barn at weird times because of my work schedule, so I often ride alone..and she is perfect. Like I said, as I am quickly finding out she doesn't play well with others...today she was doing crow hops, spooking at EVERYTHING and being a pain, wanting to take off, prancing in place ect..I could feel her in a ball of tension under me, so I got off and had to go get a lesson horse to finish the rest of the practice so I wouldn't get behind.

I have rode her a lot in that arena and she was wonderful. I'm not sure how to correct this, and get over her fear (or whatever it is) of being with other horses. Not only was it making me nervous that she was acting crazy, but it was making everyone else also. I do realize half of it is her being young and inexperienced..but I also believe her behavior is getting on the dangerous side. This is a constant thing for her..I was out riding 3 days ago and there was about 5 other people in the outdoor arena, so I took her in there, and same thing. I made her stand next to the other horses and she finally seemed to relax. As soon as the others left, she went crazy, crow hopping and all the good stuff. It's so frustrating, she's scared when there are other horses in the arena, but then she's also unhappy if they leave. I've also been told she's been shown before when she first turned 3 and placed numerous times, so I have no idea where this is all coming from.

Any advice or techniques would be appreciated.