How about make her a dessert?All have to make by yourself.
It will not be able to keep longer though.
But if she knows that is coming from u,by 100% sincere,she will feel very happy and sweet,I bet that!
Hey I just got one idea suddently!! U can make her an album which full of all your or with her photos and u can write something on each photo.
U can stay with her for every mins,u know she love u a lot,u love her a lot too,so everytime when she feel like missing u,she can just open the album and feel that u r there actually ???!!!