Mary Catherine Nivert was born 25 October 1944. She received her nickname Taffy from her elder brother, who — being unable to pronounce her middle name as a young child — would call her Mary Tafferine. Nivert began singing along with the radio in high school. She was discovered by a bartender in Georgetown after he heard her singing to a jukebox. The bartender asked if she wanted to join a vocal group, and through this she met her future husband Bill Danoff
Nivert began performing with Danoff as Fat City in the late 1960s. Initially a folk duo, the two later married and recorded four albums, the latter two credited to Bill & Taffy.
In 1970, while traveling to Taffy's family reunion, Bill began writing what would become "Take Me Home, Country Roads". The couple planned to complete the song and sell it to Johnny Cash. However, when Fat City opened for John Denver
at The Cellar Door in December 1970, they decided to show it to him. Denver, who had injured his thumb in a car crash hours before, arrived at Bill and Taffy's apartment in the early hours of the morning, where Bill, Taffy, and Denver finished the song. The next night, they performed the completed song, with Taffy holding the lyric sheet, and it went on to become a hit song for Denver on RCA Victor in early 1971, and included on his album Poems, Prayers, and Promises
, along with "I Guess He'd Rather Be in Colorado", which Bill and Taffy also wrote. Additionally, Bill and Taffy sang backup on four of the album's tracks.
Bill and Taffy Danoff married in 1972. In 1976, the Danoffs paired with Jon Carroll and Margot Chapman to form the Starland Vocal Band. Signed to John Denver's record label Windsong Records, they were most famous for the hit song "Afternoon Delight". The group released several albums before breaking up in 1981. Bill and Taffy later divorced.
Nivert lived in Washington, D.C. until 2011, where she occasionally performed with Bill Danoff and the rest of the Starland Vocal Band. She then moved to Safety Harbor, Florida.