Griffith's Valuation (the AskAboutIreland version) lists 4 McGrath occupiers in the townland of Lisnagade, Aghaderg Parish, Co. Down: Thomas, James, Hugh, and Peter.
The 1911 census indicates our GGM was born Elizabeth McGrath in Lisnagade in 1833. It seems probable she was related somehow to one or more of these McGrath families. We haven't found a birth cert yet, though, so are unsure which (if any).
(Elizabeth married Peter O'Kane around 1855, and is listed as Elizabeth O'Kane, living in Antrim, in the 1901 and 1911 censuses.)
Any information on the McGrath's of Lisnagade would be appreciated.