A setting is the frame around the painting, and like frames, most of the catalog is variation on a handful of ideas. Six of them account for nearly every ring you have ever admired on a hand.
The quiet ones
The solitaire holds one stone on a clean band and has survived every trend since the nineteenth century, which is the strongest endorsement an object can earn. The bezel wraps the stone's rim in metal, trading a sliver of brilliance for near-invulnerability, and it is the correct answer for hands that climb, lift, garden, or work a hospital shift. Low-profile versions of either keep the stone out of the way of gloves and door frames.
The expressive ones
The halo rings the center stone with small diamonds and makes it read a size or two larger, the closest thing settings offer to honest sleight of hand. The hidden halo tucks that circle beneath the stone where only side angles and the wearer know about it. Pavé lines the band itself with tiny stones and adds glitter to every gesture. The three-stone setting flanks the center with two companions, carries its past-present-future story, and visually widens everything.
Settings are changeable; stones mostly are not. If you must gamble, gamble on the frame.
Reading her file
The jewelry she already wears is a signed confession. Thin, plain bands argue for a solitaire or hidden halo. Ornate vintage pieces argue for halos and three-stones. An active life argues for the bezel, whatever the photographs prefer.
The short of it: solitaire when in doubt, halo for presence, bezel for hard-working hands, and let her current jewelry cast the deciding vote.