Mary Van Cott's father was John Van Cott, a prominent member of The Church of Jesus Christ of Latter-day Saints. She stayed faithful to that religion through her life. At a young age she accompanied her parents to Utah on the Mormon pioneer trek.

Mary Van Cott married James Cobb (or Kirby). They got a divorce, most likely before their child was born. In 1865 she then married Brigham Young, becoming one of his many wives. They had one child together. She died in Salt Lake City in 1884.

SOURCE: http://familypedia.wikia.com/wiki/Mary_Van_Cott_%281844-1884%29