I went to WDW when I was 16 w/ the choir/band. Believe me, there is nothing to worry about, teachers and administrators go overboard when protecting their students while on a trip like this. They set up (for us anyway) chaperones for every four students, so there was always an adult who knew where we were and what we were doing. Of course, PDA in the line for Space Mountain....well, they didn't know EVERYTHING. LOL
Some of my best memories of hs are from that trip! your dd will have a WONDERFUL time!