The advice to "start small and work your way up" is good. Kids are like snowflakes--each one is different! Nobody knows your child better than you do; their personality, interests, fears, etc. After reading the guidebook descriptions and watching some YouTube videos you'll already have a good sense of what your little one will go for. But, then again, she might just surprise you!
I wouldn't describe our 4 yr. old DS as necessarily timid or reticent in day-to-day life but at DL he mainly prefers the tamer attractions--well-lit, non-threatening, gentle rides. For him, things like Splash, Space, TOT, Screamin', Matterhorn, Goofy's Sky School, and THM are unquestionably OUT. He buries his face and refuses to experience most of the Fantasyland dark rides. He rode BTM once when he was 3 and did great but refuses to go again. Won't ride Gadgets Go Coaster. Didn't like Silly Symphony Swings b/c of the height. Doesn't like the talking tikis and sudden thunderstorm in the Tiki Room. He tolerates POC but doesn't like the drops or Davy Jones in the mist. Took him on the castle walk-thru and the goon's door and Maleficent's shadow frightened him. None of these things phase our 3 yr. old however... Like I said, SNOWFLAKES.
I think it would be safe to assume your daughter will enjoy rides like Dumbo, the carrousels at both parks, teacups, Casey Jr., Ariel's Adventure, Alice, Peter Pan, and Pooh. She'd probably love Disney Jr. Live. Beware of Snow White's Scary Adventures. The witch is terrifying to most kids and can spoil them for the other dark rides.
Just follow her lead and have a great trip!