B.M.
It depends on her degree. When my sister graduated from law school I got her a really nice necklace that had a charm of the law school scales of justice. So maybe find out if her school/subject area has a crest and then get her a piece of jewelry.
You could also take a picture of her and then 'frame' the picture and her diploma. We also did that for my sisters graduation - we took a pic with her in her robe and then have a frame with 3 4x6 pic spaces that show a miniturized copy of her law school degree, the picture of her in her robe and the ticket we had to have to get into the cerermony. It turned out really nice and it didn't cost very much money. She still has it up in her hallway.