How can I easily find a ring dropped in an open field?

My little sister lost her ring playing softball yesterday, it was a family heirloom and very valuable. I've tried searching around the bleachers, bench, and first base where she plays, but I've found nothing. I have a large magnet used for sweeping nails and screws from my garage floor, but I'm not sure if the silver ring is magnetic. I'm not sure exactly what material the ring is made of, but it's metallic silver. I also have a metal detector, but I don't know whether the ring will show up on it. Any ideas?