My DS LOVES this ride -- it's his absolute favorite at WDW, in fact!! He tried it for the first time when he was 7 and always goes on it lots of times (when possible!) whenever we visit WDW! Does your neice like fast rides at all? Although it's called a roller coaster, since it's completely indoors, the feel of the ride is very different from a standard outdoor rollercoaster. The only thing about it is that it goes fast (0 to 60 in 3 seconds or something) and loops around a bit (but you're so mesmorized by your surroundings that you don't even notice!)... Maybe she'll surprise you (and herself!) and try it out. It really is one of the not-to-be-missed attractions at WDW, IMO!
Have a great trip,
Sarah