We took our little guy who is 4 (and about 39.75 in. tall - the CM at the gate graciously put her hand on the height indicator to touch his head and confirm that he was "tall enough" to enjoy the ride).
He was a little nervous just when the mechanism lifted into the air. After that, he LOVED it!
On a side note, he also enjoyed Test Track, Tower of Terror, and Splash Mountain (twice!) - he begged to go on Splash Mountain more, but since we were on a tight schedule (and it was his first time ever to WDW, or any themed park such as this), we had to move on to other attractions.
The best thing is to judge what their comfort level seems to be. Don't be pushy, but point out other children (if there are any!) entering the attraction and enforce that the ride will be fun and exciting (not "thrilling").
Regardless, have fun and enjoy sharing WDW with your daughter. As a lifelong WDW fanatic, no trip was as Magical and rewarding as experiencing it with our 4-year old!