In 1870 she was listed as age 19 with her brother Isaac.

I’m not sure if they ever actually married or not. In the 1880 census, they were listed on adjacent lines but both as heads of household, with Mary’s two children David and Minnie listed as Hardin. But they were later raised as Myers. (Too bad there is no 1890 census and that so many Rowan Co. marriage records were lost to fire.)

1880 census of Rowan Co., Ky, Pearce precinct, enumerated 1 June, lists on p. 22:
family #172/191: Myers, David, 50, merchant, b. Ky Ky Ky
family #173/192: Harden, Mary, 32, keeping house; David W., 3, son; Minnie, 2, dau. All born Ky Ky Ky.