There are many possible gifts, but it all depends on a person, preferences, and budget, fo course. I can tell you about my latest gift ( from me to my sister), and maybe, you'll like the idea. I bought her a beautiful diamond ring, it was the first one she got, but before giving it to her, I sent the stone to the diamond testing lab to grade it. And when the certificate with grading results arrived, I gave her both the ring and the certificate. I think it's a great idea because knowing all the stone characteristics is interesting.