Do you mean Tinkerbell at WDW by chance? That's a real person, unless it's been changed in the past year. Zoom in on a quality video of her "flight" and it's pretty easy to see it's a real person (and surprisingly less impressive when you can see her more clearly--the lighting and costume looks weird).
If it's a show, it's likely a real person; if it's a ride, more likely to be an animatronic.
My guess is that they want to use something like this in a life-action stunt show to augment human actors.