Facts and Events
There are a number of unsubstantiated claims that her last name was Houston. However, I see nothing that supports this claim. The Houston's original home in Ireland was probably Castlestewart, Tyrone Co and some of the Houston family stories list Antrim Co. There are other claims that her last name was "Sherril". Again, I have found no one with any evidence to support this claim.
I believe that James Eakin married an "Agness" from his hometown of Drumbo, Co Down, Ireland and from within his church. Below I have listed all female children born Agnes in the Drumbo Baptismal records between 1699 - 1720. I then crossed those surnames against those in Augusta Co early settlers. I also looked at age to determine both likely immigration dates (1727 - 1735) and fertility age range (20-45). There were three Agnes that fit this description:
Agnes Anderson B: 1708/F: John Agnes Cunningham B: 1706/ F: John Agnes Davidson B: 1713 F: William 1704 Agnes Grey F: Thoms Agnes Lowry B: 1701/F: John
I believe that Agnes Lowry may be the best candidate, though the fertility range may be stretched with her 1701 birthdate. When James dies in 1765, two of the sons (Andrew and Samuel) were considered minors, presumably under the age of 21. She had a brother or cousin born in Drumbo in 1720 named John Lowry. The James Eakin family arrived in Timber Ridge in 1742 and their immediate neighbor was a John Lowry who arrived at the same time. Certainly more investigation is needed, but this is a promising lead to pursue.
Other Agnes' born in Drumbo:
1704 Agnes Beck F: John 1713 Agnes Catherwood F: Hugh 1706 Agnes Clegge F: Elias 1707 Agnes Conn F: Robert 1718 Agnes Corbet F: Robert 1702 Agnes Little F: Christopher 1709 Agnes McClintsy F: Edward 1702 Agnes Poter Samuel 1704 Agnes Richy F: David