It is possible that she is the same person as Mary Gore, wife of William McIlvain, and that Jefferson Moore was her second husband. Her son Pliney’s death certificate lists his mother’s maiden name as Mary Gore. But Lucy and Jennie’s death certificates both give their mother’s maiden name as Mary McIlvain, so most likely the informant on Pliney’s death certificate was mistaken.

Bath Co., Ky marriage book 3 lists the marriage on 18 Dec 1860 of James Jefferson Moore and Mary Jane McIlvain.

I cannot find this family in the 1870 census.

1880 census of Bath Co., Ky, Owingsville precinct, enumerated 28 June, lists on p. 47 as family #423/425:
Moore, Jefferson, 50, farmer; Mary, 50, wife; Lucy, 18, dau; Plinie, 17, son; Jennie, 16, dau; Lizzie, 13, dau; John, 10, son. All born Ky Ky Ky.

Jefferson’s brother David is recorded four households above.

In 1900 Jefferson was recorded with his daughter Jennie and her husband William Toy as Jefferson Moore, father-in-law, age 69, born July 1830 Va Va Va, married 40 years. He has no wife in the household.