well....coming from somone who went to disney as my senior trip when i was 18 i can try and help....for starters remind her that even though it is disney....she still may not wander off alone anywhere...esp towards the PI area at night should they head that way....remember to always have emergancy contact info....to keep hydrated and keep sunscreen handy ( i wore my hair in pigtails one day and my scalpe got really burned ouch
) take a camera for lots of pictures! also to get a look at park hours before she goes and look at what parks have emh and possibly plan around that...lastly just remind her to have a blast!