We are about at our wits end with our mare. She works awesome when we run barrels at practice (multiple arenas). When we get to a show she runs straight up the fence at the first.  Any suggestions? We have her worked on regularly so I don't think pain is an issue because she gets multiple days a week and does perfectly fine. She is a bleeder. 

Can you give us just a bit more info?

You say she works great in practice. Is that only slow work or do you run her in practice too? Do you circle or come running through the gate in practice?

At a show.  Do you circle or run from the gate? Do you do warm ups/time onlys at a show? If you do are they fast or slow?  Will she go up the fence at any speed at a show - or only when you run?

One that goes up the fence can be super frustrating.

If this is a horse that was previously working well and then started running up the fence I would find a good lameness vet and have her checked out thoroughly, look closely at hoof back ace and shoeing. 
If the vet doesn't find anything in a lameness exam I would u/s soft tissue in the RF and RH leg.
a sore horse will usually work well at home or even in an exhibition because they know they have to work. 

My friends horse was doing this. Found out she was a bleeder. Vet put her on lasix, helped her a ton.