Hi Keri,
Taking your child to Walt Disney World for the first time is such a magical experience. I know you'll create many happy memories!
Your question is a tough one. Every child is different. I have an 8 year old who still gets frightened on some attractions, while my 2 year old will try just about anything. I can give you a list of some attractions to be wary of. You know your child best, and you know what she can or cannot handle. Thanks to modern technology you can often view these attractions by searching at YouTube.com.
Magic Kingdom: Pirates of the Caribbean, Haunted Mansion, Snow White's Scary Adventures, Stitch's Great Escape (although she may not be tall enough for this attraction anyway)
Epcot: Honey I Shrunk the Audience, Maelstrom
Hollywood Studios: Sounds Dangerous, Fantasmic!, The Great Movie Ride
Animal Kingdom: It's Tough to Be a Bug
There are also a few attractions that have height requirements. To see those, click
HERE.
Hope this helps. Have a magical vacation!