As she's in PC already, I would just increase the number of PC activities that you do (we literally went to everything beforehand as my daughter was very anxious first time), so your daughter gets to know everyone really well before they go.
I'd also chat to the leaders about how they organise camp so you can prepare your daughter. If she's worried about not being 'up together' in terms of knowing what to expect at camp, I would ask if they will be doing any pre-camp preparation for those that have not been before. Our PC often ran some unmounted Horse and Pony Care Quiz sessions at this time of year. The Quiz is run nationally in set age groups, with a big final at PC Champs, and is all about looking after your pony and their equipment, and there are certain sections covered most of which can be learned and a badge is taken eg mucking out, equipment safety, feeding, yard safety - all good basic stuff ideal for knowing what you're doing at camp later on. Nearer camp time, they may offer camping badge if they've a lot of inexperienced campers for example.
At our PC for camp, they tend to split them up into packs rather than friendship groups for the horse and pony care part of it, so they have a very experienced leader, an almost as experienced second, and then the rest of the pack will be younger. They'll gain points for their pack for looking after their ponies well, keeping them well groomed, clean tack, and everything stored away neatly equipment wise, and keeping the yard area tidy, so you'll find the leader and second will be dab hands at doing their ponies and know exactly what is expected so when they've done theirs they'll have time to help and show the less experienced who obviously will be slower, as it's a team effort for points. And there will be a trophy for the best/most improved individual and also sometimes best first time camper, and 1st, 2nd, 3rd etc rosettes for all groups at camp.
For riding they'll put same ability together so mostly she'll ride with her friends she's already riding with (again lots of rosettes to be gained), and they'll likely be taking a few badges too, for badges and for evening activities they'll divvy the groups up according to activity so she'll be working with others not necessarily in stable group or friendship group. and and for sleeping they'll pop friends together in the same tent/cabin/share of horsebox.