TYING UP HORSE! When will her AST count go back to normal?

My Appendix QH Mare tied up for the 4th time (In 2 years) about 9 days ago. The first time she ever tied up was in December of 2005. Blood work was taken- AST 3800. We changed her diet to a no carb, high protein/fat diet and she was doing well on it. Nothing has changed and on Tuesday of last week, she tied up again. She is a barrel racer and has been running every weekend since May with lots of work in between. She tied up while we were simply WALKING on a trail ride. Nothing extreme, most of it was an old logging road. We did another blood test again and her results sky rocketed from the first time (in 2005. Her AST was 33,400. YES, Thirty Three THOUSAND. It was obviously an extremely bad episode and I don't understand why. Normal work load, No change in her diet. HELP! We have State Finals this weekend. It's about a 4 hour haul. My vet has given her some dantrolene sodium, ace and banamine (Not all together) as a preventative. We are re-doing blood work today to make sure her levels are low enough (looking for below 3000.) I need advise. Is it diet? Is it something else?