That is what I was thinking, John and Alexander and Mary Helen were the one's to look at first.
I did come across this for Isabella
Scotland Births and Baptisms
Name -Isabel Lamont
Gender Female
Christening -Date 06 Dec 1778
Christening Place , RUTHERGLEN, LANARK, SCOTLAND
Birth Date -26 Nov 1778
Father's Name -John Lamont
Mother's Name Helen Armour
I looked up Rutherglen and it is a small town near Glasgow, so this could be a possibility but the birth date does not match with that of her death record. Which works out to 1781