Hi Cheryl,
This question is so timely for me! We just returned from a visit to Disney's Fort Wilderness Resort with our 7-year-old daughter and I looked into this exact same question.
In order to participate in the trail rides on the horses at Fort Wilderness, a child needs to be 9 years old, so your daughter will not be able to do this on this trip. However, she can do a
pony ride at Disney's Fort Wilderness instead. To do a pony ride, the child must be 2 years of age or older, weigh under 80 pounds, and be under 48 inches tall. For a pony ride, she won't be on a horse by herself on a trail, but rather on a pony in an enclosed area, which you or another adult will lead around. Pony rides are offered near Pioneer Hall daily from 10:00 a.m. to 5:00 p.m.
There is so much to do and see at Disney's Fort Wilderness, Cheryl. Have a wonderful time exploring it all, and please do not hesitate to ask if you have any further questions in planning your trip!