Investigate whether she was the daughter of Anne Crake or Ann Huetson. On FamilySearch (
https://ancestors.familysearch.org/en/LCT8-6XB/mary-coulthard-1749-1819) she is shown as having been born in 1749 - and there are definitely baptismal records for a Mary daughter of Edward Coulthard born in 1749 (in Dalston). Actually, they both might be true...perhaps she was born in 1742, but only baptised in 1749?
Early Life
Mary was born c. 1742 (her age was given as 77 in 1742 when she died).
There is a
Burke's entry on Coulthart of Collyn (in Dumfries)
1; Dumfries being on the other side of the border from Cumbria suggests that there could be a link between these families.
Footnotes
[1] Burke's Landed Gentry, New Edition (1847), Volume 1, Page 270