Surprisingly our daughter did not complain about wearing hers when we went back in '97 in May. I was really surprised, too. She has since had back surgery for rods and that wasn't a problem for us the last two trips.
I would just use the hints the other's have suggested, and try to give her some pool time to be out of it for awhile since she will still be getting used to it. Our daughter had to start wearing hers at age 5, so we know about the reluctance factor.
Also, have the doctors evaluated her for any possible other neuro complications like hydrocephalus, and Chiari Syndrome? The two together are what caused our daughter's Scolisosis. I would definitely ask them for all of the possible causes of this at an early age. Especially if it was one or both of these, a possbile shunt may be in the works.
Good luck on your upcoming trip.
Kim
P.S. Does she seem to have any complaints about her energy levels? We had to definitely take Faith in a wheel chair due to endurance problems each time we've gone with her. You might want to keep that in mind, or if your daughter is small consider taking a stroller for her.