Most Helpful Girl
You could make up a box, putting things into it that remind you of her, maybe a handwritten letter saying how special she is, or some pics of you guys together.
If you can, may be stay up talking to her until midnight, then as it become her birthday, send a sweet message asking her to come outside, then be waiting on the doorstep with the box and a kiss.
Most Helpful Guy
Write her a letter, handwritten, just telling her how amazing she is and stuff, maybe put a few things that remin you of her and vice versa... give it to her now and tell her not to open it until you say.
Then send a lovely text and midnight.. but end it with something like "you can open it now"