"Mildred Couper, prominent American composer and pianist, was one of the first musicians to experiment with quarter-tone music. She was based in Santa Barbara, California, but her music and influence were felt around the world." More.
There's a remarkable photo of Coupler, Stravinksy, Boulanger, and a nun here.
You can hear her Rumba for piano here.
Kudos to the site's owner!