I know the design style she likes and I know the type she hates - any ring that has multiple tiny stones around the band or around a main stone. She'd make me watch say yes to the dress on weekend mornings and would give commentaries on their choice of rings and dresses which is what set me in the right path to know what she does/doesn't like.
I'm probably overthinking a lot more than I need to. I guess my main focus right now is where to purchase it from. Size can be made on the spot when deciding on a purchase.
It's hard to check her jewelry because she rarely wears any. she has a ring on one finger that she's had for years because of its unique design. this morning when I was leaving for work the earrings she had in were these

little NES controller studs. My aunt bought her diamond earrings last year but she doesn't wear them unless she's going out somewhere "fancy" lol.