Does she have a Nintendo DS? if so then try :-
Nintendogs (varoius versions)
42 all time classics (great multiplayer games )
Big Brain Academy
Mario Kart DS
Imagine Fashion Designer
Kirby
My Sims
Animal Crossing
Zelda (swords and wizards type thing)
On the non games front clothing / shoes are always a winner so give either cash or vouchers.
If she is artistic try bead kits, Scoubido kits (sp?) paint sets (Toy & Hobby do some really good things here go to get some ideas but try to buy elsewhere as it can be expensive)
The latest NOW compilation CD or one she may not have,
DVDs loads to choose from here Princess Diaries, Step up, Honey , Devil wears Prada, Uptown Girls (Weepie), She's the Man, What A Girl Wants etc..