My DD14 has T1 diabetes and was diagnosed at age 9. Have snacks and low treatments with you for lineup lows so you won't have to leave a long line. FRIO bags are invaluable for keeping insulin at a cool temperature in Florida's heat. Always keep her glucometer with you.....almost all of Disney's rides allow you to bring bags onto the ride. The first aid stations in each park will take any extra insulin you pack and keep it refridgerated for you. We always keep a DKA kit at the first aid station but my DD is using a pump. Be aware that in the extreme heat of Florida, being overheated can mask a low since they have a similar presentation.....when in doubt, check her sugars.
Regarding the food at Disney, the restaurants do not provide carbohydrate information which I find extremely frustrating in trying to regulate her blood sugars....less so now that she is on the pump but, prior to this, trying to measure carbs for a strict diet was challenging. When we first travelled after diagnosis, we spoke to the chefs several times but found them to be very limited in being helpful......that being said they can let you know if there are any added sugar to the recipes they use. My best advice regarding nutrition is to bring a pocket sized book such as Calorie King. You should be able to use this as a rough guide to guessing how many carbs are in a serving size.
Good luck and have fun! She will be fine.