Make a 'treasure box'.
Buy lots of little things that she will like or that are special to the two of you.
Also put in things like chocolate, framed photos, mix CDs, nail polish, stationary, etc.
And sometimes things that might be a personal joke between the two of you.
Maybe if shes artistic you could put in a paintbrush, or if shes a bit girly put in a plastic princess tiara lol.
Just make it really special- little things that say alot about her!
( things she likes, things she hates, memories, things you did together etc)
just think creative and symbolic.
then put it all in a box and cover it with photos of you & her or of things she likes
(Usually this wont cost very much- you can buy most of the stuff at a cheap shop. So if you have money to spare you could put in a dvd- perhaps her favourite movie, or otherwise movie tickets, a free day at a spa, etc. just make it work with your budget!!)
good luck!! xx