A hinged piece is one of the more practical gifts in jewelry: no tools, no instruction, no assistance required. The recipient can put it on and take it off independently from the moment they open the box.
Stone Story
Cubic zirconia exists because the optical properties of diamond turned out to be reproducible in a laboratory. It's a synthesized crystalline form of zirconium oxide, engineered to simulate diamond's appearance.
Visually Speaking
If you know she tends toward quiet, precise jewelry, a smaller diameter is the right call; if she wears pieces that move and draw attention, size up: diameter is the variable that determines which kind of hoop this is.