Hi, wish I did know ... I've got Meins in the St. Boswells area at that time. But Mary Mein is so common a name for that area, as is Turnbull! (I've got Turnbulls too, but in the next century, in Lilliesleaf, and only peripherally ...)
Any idea who Mary's parents were?
According to the Scottish naming custom, the second son would have been named for her father and the first daughter for her mother. But that "William Turnbull b. c1742" is out of synch with the rest of the kids' ages ... curious. Are they baptismal dates? Because that's a long lag between the births of the first two children if so.
Does it fit with any known candidates for her mother's name to be Frances?