Unless you can think of something personal and special that she would appreciate from you, I second the GC to AE or Aero. That's what I would have wanted at her age.
I tend to spend more money when I get a gift rather than a gift card. So I'd probably give a $40 gc. But if I'm buying earrings or books or whatever, I'd probably spend $50ish.
Re: NBR gift
What does she like and what do you want to spend?
The first thing that came to mind were earrings.