This is my grandma, showing off the stretchy ring BLING she got for Christmas. She's always had an extensive jewelry collection, but in recent years her arthritis has made it too painful to wear her rings and too difficult to operate some clasps. Read on for some of the options for people who love their jewelry and hate their arthritis.
Stretchy rings/bracelets (Potpourri) - these rings have made their way into my grandma's regular rotation. There's matching bracelets for some and they slip on easily. (We got her the pearls and the ones with the single gem in the bottom right, not the crazy ones made of sticks) The ones from Potpourri are fairly inexpensive, I have seen similar ones in specialty stores MUCH more expensive so do some comparison shopping.
Magnetic clasp converters (shopping search) - I saw these on TV ads. They look like a person with arthritis might need assist with initial setup but then they should be independent to doff/don. I haven't personally tried them, so I can't speak to the strength of the magnets, but they're probably not strong enough to hold up heavy jewels like pearls.
Wire chokers/bracelets - These are pretty common, if you can convince an adult to shop with the preteens to get jewelry. Just look for the necklaces without clasps in U shape.
Bracelet fastener (bracelet buddy) - I was intrigued by this device when it first came out, but it may be too complicated as adaptive equipment now that other stuff has come out.