Hi Faith!
Thanks for your question. What a cool Mom to bring your daughter's friend along to the "Happiest Place on Earth!" I'm sure your daughter is ecstatic, and sharing special memories with not only her family, but her friend as well, is something your daughter will never forget.
No forms or special letters are required at
Disney World or any of the
theme parks. Disney understands that guest groups are very diverse, including family members, caretakers, friends, co-workers, or even fellow neighbors. Your family will be her caretaker during the trip, and that's good enough for Disney. So long as she's included on your reservation (if staying in a
Disney Resort hotel), or you have tickets for her at the theme parks, you're good to go!
May you and your family (and daughter's friend) have a magical time at
Disney World!
Terry