Using the McKercher.org web site indicates there was a Mary McKercher born 9 April 1713 at Aberfoyle, which is not that far from Drymen and age probably fits. Father was a John McKercher and mother an Ann Graham.
Do not get put off by the Mckercher spelling on this site. All the variants were adjusted to this version for search purposes.
No details on marriage or children are listed though.
Allan
