Give her (or him!) a personalized initial necklace. I have them in many styles and fonts, including an elegant Script Initial Necklace or modern Bauhaus Initial Necklace. Get one for yourself to commemorate the accomplishment for both of you!
How about a whimsical charm? Give them an Apple Charm (for the student!), a shooting star (on sale!) or a soaring bird necklace.
Able to splurge? How about a Petite Diamond Disk necklace or some Rough Diamond Earrings?
Post and let me know what gift you've gotten for your grad and congrats!