How far away is her b-day?
If you have some time, have a bunch of pictures/ticket stubs/poems/letters or any memory type things printed together in a real professionally done book
A place like http://www.lulu.com/ does great small run prints of pro-quality self published material for decent prices. I think even cafepress.com does that sort of thing too. Lasts forever and I swear there's no girl in the world who would not like to receive that Except for maybe girls heavily prone to paper cuts and doctors advise them not to be near books. But other than that small minority, all girls would love it.

Either that or a Coca-Cola barbie set!

But that might just be me...

So I'd go with the personalized book thing.
Or any of the personalized things you can get printed up at a cafepress type place.
Maybe go elaborate with a whole set of personalized merch like mugs and shirts and clocks and mousepads and whatnot!