Margaret was an only child, born in Berkeley, California to mother Margaret Orchard and father John Melhase, who worked as a geologist.
During her time at UC Berkeley, Melhase was a member of the Berkeley Folk Dancers and edited the group's newsletter. She met mathematics professor Robert A. Fuchs at a folk dance, and the two married in 1945 and had three children. She and her husband moved to Los Angeles. She was a supporter of social causes, organizing marches for agricultural workers and housing and aiding immigrant Laotian families in Los Angeles.