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.
Made With Purpose
The friction back, also called a butterfly back or push back, is the standard post earring back. It has a small metal finding with two spring-tension wings that grip the post when pressed on, holding the earring in place without a locking mechanism.
The Perfect Gift
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.