Wild Mare-NEED HELP FAST?

So my mare gets plenty of exercise (six days a week) but continues to be wild and VERY VERY spooky. She gets worse when we jump, even if it's just a tiny corssrail. After the jump she completely takes off and then gallops around the arena like an idiot spooking at silly things. Punishing her for running away by stopping her and backing her up does nothing but upset her. She's really sensitive and absolutely loses it when you get rough with her. I'm thinking that she's being this bad because she's nervous...someone obviously beat her up before I bought her. Any suggestions on how to calm her down??? Some people have suggested hormones but she's really not a mareish mare. She has a very even temperament and gets along great with other horses. What should I do?!! I'm getting to the point where I'm really frustrated after every ride andI have a horseshow in two weeks! I need a solution FAST!