This is an opportunity to appeal to her better self, or to show her something about your better self. Think about her better qualities (there must be something) and buy something that acknoeledges them in a small way - or come off your own to find/buy something that shows her who you are. One year I made my MIL a patchwork quilt themed around their interests in travelling & country music, and the sun has shone outta my bum ever since then LOL. Obviously $20 might not get you very far, but even a well chosen book shows you have put thought & effort in.