Your mystery Mullinax, Sarah, is probably actually Mary Emily Mullinax (though she could also be Mary's sister, Martha, who married William Caylor).
Mary Emily Mullinax married William P. Dunn. Originally someone had different parents for him, but I think he is William P. Dunn, brother of Rhoda (Dunn) Headrick, who is John Scott Headrick's wife. My reason for thinking this about William P. Dunn and Mary Emily Mullinax, is that, right after the marriage, a couple of newlyweds named William and Mary E Dunn are living right beside .
She is one of those Mullinax children whose household was split up, with the children scattered among nearby Caylors and Dovers in 1870. The parents had disappeared or died: Malinda, the biological mother, between 1851 and 1856; Benjamin, the father, in 1869. Mary, the stepmother, lived until 1927, and remarried Charles M. Dover in 1869--so some of the children are found in the Dover household.
Mary Emily Mullinax PID -- think of her as "probably a.k.a. Sarah":
LKKH-LVB
