Hi Suzann ~
Those are excellent questions and concerns. The Walt Disney World Resort is much larger than Disneyland with lots of stimuli everywhere including a lot of noise. That can be overwhelming for some Guests with sound sensitivities.
One thing I've found that has helped my son is noise-canceling headphones. These work great for him especially during the fireworks. If you know a loud noise is coming up, warn her so she'll know it is coming.
Another option is ear plugs, if your daughter will tolerate them. Some kids do not like them so I would try them prior to your trip. If these work well for her, I'd recommend the ones that are attached with a cord so that she won't lose them as easily. Make sure you bring a couple of backup pairs just in case.
Sometimes my son likes to listen to music through earbuds to act as "white noise" when he feels it is too noisy in the parks. We make sure we have his favorite music downloaded on my phone before we head out to the parks.
I also recommend giving her breaks. There are lots of areas available throughout the parks where you could give her some down time to take a break from the noise. If you feel that would help, ask a Cast Member where the nearest area is located.
If she has a hard time tolerating fireworks presentations (even with noise-canceling headphones), you could try watching from a location a little further away. My boys love watching the fireworks at the Magic Kingdom on the
Pirates & Pals Fireworks Dessert Voyage. It is a fantastic experience from beginning to end and combines some of our favorite things: yummy desserts, character experiences, a voyage on the high seas (okay - the Seven Seas Lagoon), and it is a great way to see the fireworks without the loud noises.
Wishing you minnie magical memories :-) Allison V.