So really, think about what you would do if the $200 you have were gone. Or if you didn't have that saved up and camp wasn't an issue and your DD accidentally broke a neighbor's window throwing a rock at it. WWYD?
I will say that your last post about DD2 attitude is appalling to me. She is saying she is sorry but she is certainly not acting like it. Whatever you decide to do with the money that was earmarked for her camping trip, she has to start making a plan (probably with your help) to repay DD1 and start working on it immediately. Yes, it can be tough to find odd jobs, but with a little initiative she can do it. My youngest brother did odd jobs (mowing, cleaning, etc.) for several people in the summers to earn money at that age. I really think this is the first thing you need to address as she can't sit around shrugging her shoulders and continue as if nothing has happened.
I don't have kids yet, but I do think presenting it to her as she can come up with a plan to repay in a reasonable (for a 10 year old) amount of time and start working on it immediately and show that to you before you have to pay for camp or the money set aside for camp can go for the guitar now. Or if you are willing/able as another poster to suggested to charge the guitar and have your DD2 pay back with interest, I would consider doing that as well so DD2 can still go to camp. Again, back to the question I quoted, WWYD if this had happened with a neighbor who demanded DD2 replace it immediately and there was no money set aside for camp?
And I also agree with those who posted about needing to get DD2 emotionally involved. They said it better than I did, but again, no more of this mouthing "I'm sorry" but not doing anything about it.