I actually work for Childrens Activities at the Grand Floridian. A five year old at WTP should be fine as long as she isn't affraid of the Mad Hatter. He is usually the one thing that scares the young children.
If she is use to being left without you, that is also helpful. The one thing we really try to encourage is getting to the check in early ( we start checking in at 1:00), this way the child can warm up to the other children and start to get use to the noise. Yes Tea can be very noisy. We book up to 28 kids at tea, all those kids and the Mad Hatter equal allot of noisy.
Let me know if I can help you in any other way