Tips from one who broke a leg on a mission trip and was a youth director with a broken leg in the summertime and the only event I didn't do with the youth that summer was the high ropes adventure.
1) rent, borrow, buy a wheelchair or ecv. even a regular wheelchair will work. Consider one that has the leg support and can be elevated. Bring along a pillow for elevation.
2) where are you staying? consider someplace very close so that you can get back to the hotel for a rest (maybe even twice a day) When in the room elevate, ice, elevate--lay down not sit. If you don't (and I am assuming she has a cast) you will be miserable and even unsafe should you leg swell in the cast.
3)Talk to the orthopediast before leaving so that pain meds and the group will know should you need to call because you are having problems. Also check with your insurance about how to obtain care in an emergency. The orthopediast knows you break, where you are in the healing process and will be able to advise you about rides- even if they personnally can't someone in the gorup will have been to WDW and/or
Disneyland
4) eat, drink plenty, have help to bathroom and on and off rides. There will be several that you will be able to ride. The kids will love this as your party is allowed to stay together in most cases. Downside, you miss the cool queque's.. Have a stash of advil unless contraindicated.
5) bring or buy trashbags for showers and water rides if they will let you on them. Also bring icepacks, you will need them after being up a while on a broken leg.
Any other questions, you can PM me. Been there, done this, didn't follow instructions and paid later as well (all temporarily). Have a great trip