Hi Faybra!
Rent an electric scooter! Walking around Walt Disney World while 8 months pregnant in August is a rough combination. I know, I've been there. Since it will be hot and humid, her feet will probably be more swollen than usual.
An electric scooter is a great idea to minimize the amount of walking she will need to do. These can be rented at all of the parks and at Downtown Disney.
Make sure she is well hydrated. Drinking lots of water is important when you are pregnant, especially if she is going to be in the heat. You can ask for complimentary cups of ice water at any location that sells fountain soda.
Wear comfortable shoes for the time that she is on her feet. My favorite shoes when I was pregnant (and even now) are my Croc flip flops. They are so incredibly comfortable and airy so my feet don't get hot. I wear these every time I go to Disney World.
Rest! If she is getting too hot or too tired, suggest that she sit down in an air conditioned restaurant or gift shop while the rest of your group goes on an attraction, especially an outdoor attraction. Get her a strawberry frozen bar and tell her to relax for a few minutes.
Take advantage of the pool. Swimming or just floating in the pool is so comfortable when you're pregnant. If you are staying at a Disney World Resort, take a couple hours off in the afternoon to lounge poolside and take the weight off of her feet and back.
Shop! Browse the shops for an adorable onesie to bring back home for the baby to be, or even a Mickey or Minnie plush doll as a souvenir.
Most of all, have fun!
Have a magical day!
Leslie