Hi Stephen,
There are many rides that are appropriate, and loads of fun, for a three year old girl. If you head over to the
Disney attractions page, you'll see that there is a box to click for height requirements. Just click her height and you'll see what's available.
When my own daughters were that age, they loved It's A Small World, Peter Pan's Flight, the carousel, Winnie the Pooh, Buzz Lightyear's Space Ranger Spin, the Country Bear Jamboree, the Tomorrowland Speedway, the teacups, the Jungle Cruise, Pirates of the Caribbean, and much more. And don't forget all the fireworks, parades, shows, character greetings and character meals that hold great appeal for little ones.
Have a great time!