Agnes Coolbrith joined the Church in 1832 and, after staying with the Smiths in Kirtland for a time, married Joseph's younger brother Don Carlos in 1835. They had three daughters together, the youngest of which was Josephine Anna Smith, who later became known as Ina Donna Coolbrith. Don Carlos and one of the two older daughters died in Nauvoo of malaria.
Five months after her husband's death, Agnes married her brother-in-law Joseph. (This marriage is not mentioned on the Church's website.) The marriage warranted a cryptic note in Masonic code by Brigham Young, an enthusiastic journal entry by Joseph, and a rumor against the prophet that sent Emma into a tizzy.
Cousin George, DH#3
After Joseph was killed Agnes ended up marrying George Albert Smith, a cousin of her first two husbands, a member of the Quorum of the Twelve, and husband to another woman, but ultimately left George during his preparations to move to Utah. Instead, Agnes left the Church and went to Saint Louis, where she married printer and lawyer William Pickett, with whom she had twin boys. They soon moved to California where Ina would gain fame as poet laureate.
Agnes hid her Mormon, polygamist past for the remainder of her life, though a letter to her nephew Joseph F. Smith reveals a deeply felt tie to Joseph and Don Carlos' family.
Why did Joseph take Agnes on as another wife? Was it simply a Levirate thing? It definitely doesn't meet God's requirements for the New and Everlasting Covenant. For starters, Don Carlos and Agnes had probably been sealed - I find it difficult to imagine that someone as inner-circle as the prophet's brother would have been left out of the sealing game. Secondly, she was most definitely not a virgin. Third, it's doubtful that Emma gave her permission otherwise she probably wouldn't have initiated an investigation of rumors about Joseph's licentious dealings (or she could have been trying to cover them up). And finally, where are the Joseph-Agnes babies? They raised no "seed." So why should anyone believe this marriage was sanctioned by God?