Is it an option to let her bring a friend? My son was absolutely miserable when we brought him two years ago (he was 11 at the time). He whined and complained almost the whole trip, he was only interested in the roller coasters and everything else was "boring" to him. It didn't help that his sister was only 4 at the time so we had to spend a lot of time catering to her and going on the "baby" rides too. My husband and I spent almost the whole trip separated, one of us going on the "fun" rides with DS, and the other going on the "baby" rides with DD. It was a really fustrating vacation.
Last year I let him bring a friend with us and it made a world of difference. They were old enough to go off on their own together as long as they remained in the same park, and DS was like a different kid. He had a great time, and we still spent plenty of time together swimming, meeting up to eat, fireworks, etc.
I know this isn't an option for everyone, but just something to consider. It really made a huge difference to us, and everyone had a much more enjoyable time last year. He's planning on bringing the same friend again this year, and we're really looking forward to it.
Good luck, and have a great trip!