Hi, L.,
My son has the same problem (he's 10) and we took him to a urologist to figure out what was wrong. Turns out that he had gotten so used to "holding" his pee (so he didn't have to stop playing) that his bladder needed to be retrained. He was only emptying half way, rather than completely emptying the bladder. So he had to retrain his bladder to recognize the feeling of needing to go potty.
So, for four weeks, he had to go to the bathroom every two hours, and we had to write down the results (peed, pooped, tried but couldn't). Even if he couldn't, he had to stand there for two minutes, trying. After dinner, he had to sit down for five minutes, to poop. And we had to keep track of when he was wet, day, night, just drips, very wet, wet bed, etc.
Before we took him, he was wetting the bed almost every single night. During the retraining weeks, he did it once! It is SO much better now.
Although we don't write it down anymore, we still make him go every two hours. OH, and before bed, he has to do double elimination. He goes to the bathroom, then gets ready for bed (teeth, story, jammies, etc.) and right before getting into bed, even if it's only been five minutes, he has to go try again to pee.
I don't know when the camping trip is, but maybe you can start your daughter on the retraining program. (But have her take a big kid pull-up, just in case)
Good luck! And, you know, the urologist told me that the only greater trauma for a child than wetting, is losing their mom. That's how damaging it can be, pyschologically. So maybe you could tell her about the responses you got to this post so that she knows it's a MUCH more common problem than is realized. She probably has classmates who are faced with the same dilemma right now, in regards to the trip!
Blessings, J.