Hi Ken.
This is a great question and I love how thorough you are being with your planning!
I can tell you from personal experience with my kiddos, the height requirements are strictly enforced. Safety is the primary concern of Cast Members. If your granddaughter isn't quite tall enough, they will not let her into the
attraction. My son is on the shorter side. We found some tennis shoes with thick soles and we actually practiced standing up nice and tall. It was a magical day when he was tall enough to experience
Big Thunder Mountain Railroad! The thick soles ended up being a bonus because they were super comfortable for him as he walked all over
Walt Disney World Resort.
There are height guides outside the entrance to all attractions with height requirements. In most cases, there is a second height guide as you get closer to the attraction.
As a mama bear, I think I was more disappointed my kiddo couldn't enter an attraction, than he was. So - definitely, put on a happy face and move to the next attraction. There are magical memories waiting to be made!
Thanks so much for sharing your question with the Disney Parks Moms Panel. Please let me know if you need any other information as you plan your magical Walt Disney World Resort vacation.
Kari