Hello Patricia!
Your question hit home for me as I have a daughter that is now vegan and I had the exact same question! As we are planning for our upcoming trip, I have done research, and I have been delighted to find an extensive array of choices for the vegans in our lives.
First and foremost, always talk to the Cast Members at the dining location and inquire about vegan offerings. Some places, such as Trail's End at Disney's Fort Wilderness Resort, have options that are not necessarily on the menu. In my experience, the culinary professionals across the Walt Disney World Resort take pride in meeting the dietary needs of all guests.
A few of the vegan delights awaiting your granddaughter include:
There will be much for her to explore across the World! OH...I almost forgot to mention, the famous Pineapple Dole Whip is also vegan.
If you have more questions, come on back tot he Disney Parks Moms Panel.
See ya real soon,
Anne