Listen for Jeannie Robertson (deceased now) -- one of the best Scottish traditional singers. Also her daughter Lizzie Higgins. And Susan Reed who recorded in the forties had a great voice. Cindy Kallet, who is alive and well. Kathy Kallick in bluegrass. Dolly Parton has a beautiful voice if you can wade through her material. And the singers in Out of the Rain, a defunct Bay Area band, two of whom are female, have gorgeous voices. The women of Charming Hostess have the best vocal control and flexibility of anyone I've heard singing traditional material. Janet Russell is a lovely singer, as is Christine Kydd.