Well since she's an artist I'm sure that she will be happy with anything creative that you can come up with. Write a sickeningly cute 30 second song for her, write a short story (or god forbid a poem (if you do a poem, get a beret and striped shirt for when you read it to her)), make four cardboard signs that say: I, Love, You, <3 then take them into a photo booth and hold each one up for each picture, get a silly but endearing photo mug made for her (maybe work an inside joke into it), get a large surface from some where (salvage) and spray paint a heart onto it or something sentimental as a large art piece to go on the wall (even if you're not too artistically inclined it will still look great/impressive due to the large scale) etc... those are all cheap or free. YOU CAN DO IT!!! And then maybe you will [i]do it[/i]?