The best way to know for sure is to take her to the bike store and let her try out a few. A test drive is critical. You can probably get a decent bike at Sears or someplace like that and Huffy is a pretty popular children's brand, but bike stores have reasonably priced children's bikes that can be measured to fit and grow a bit with her. Also, there's usually a repair shop in the back in case you need something fixed or, if you're as mechanically challenged as I sometimes can be, you need someone to put on or take off training wheels. Even if you want to surprise her with a bike, let her test drive a few to see what will work for her and get an idea of what she likes. You can always put a hold on it and come back later to pick it up.
jj