well here....usually whatever you buy a girl they sometimes say they like it but dont really...so ask her to come shopping with you so you know what she wants and she will like it...in the meantime just do something very sweet for her that she would like....like buy her a case of chip's ahoy! those are sweet!
Diamond earring at a smaller size can be gotten at a good deal. Just figure out what she has jewelry wise before you buy her something. She may want/need something like earrings, bracelet.