Hi Patricia,
There are many families with children on the Autism Spectrum who have had excellent experiences with
Disney vacations. I'm one of them. You may want to visit the independent website
allears.net, which has several stories submitted by parents who have successfully traveled "The World" with their special kids. Search "autism" from the site's home page. Many families offer suggestions and tips that they found helpful.
Once you arrive, I would suggest that your first stop is the Guest Relations Office at whichever park you start out in. (At the Magic Kingdom, Guest Relations is located inside City Hall, which is on the left as you enter the park.) There, explain your daughter's needs and your concerns to the Cast Member (CM) who assists you, and s/he will issue a "Guest Assistance Card" (GAC), which will enable your family to enter attractions through an alternate entrance. In most cases, this will greatly reduce waiting times.
The card will only need to be issued once, and will be good in every park for the entire length of your stay. Some families chose to bring along a doctor's note if their needs are not readily apparent. Most special needs families that I have spoken with are very satisfied with the accommodations available at Disney. You should find that the GAC is a discrete way to help your daughter have a vacation that is as magical as she is!
Have a wonderful trip!
Tanya