Todd,
You are going to have so much fun! I think the best time to go is September/October, but early May is a good second option. Crowds are smaller because school is in session, but the weather is great!
As for restrictions on rides, there are a handful of rides in each park that require a minimum height to ride, and a couple more that have a minimum height required to ride with an adult. The height restrictions change by ride, but are usually 40 inches.
These restrictions are listed on the park maps that you pick up as you enter, as well as on the individual attraction web pages, as you can see here on the page for
Big Thunder Mountain Railroad.
Remember that Disney World is largely focused at families, particularly ones with younger children. So know that a majority of the attractions here are going to be appropriate for your daughter.
Have a Magical Vacation!