My grand kids aren't old enough yet! But I'll watch this post and glean the infor for later! LOL!
I would say it will depend on her skill level and her desire to ride. Are you looking on getting her into Raod riding? Trek makes a nice SMALL road bike called a KDR 1000 that is a full on Road bike. Trek also has a KDR 7.2 FX which has nearly the same specs at the Adult version of the FX. I would be inclined to look for the FX, due to the upright nature of the frame.
Chris