There are only twenty four years between the first and last recorded children, so it is quite possible. If the mother was 18 - 20 when the first was born, then she would be 42 - 44 at the birth of the last child. Quite within the bounds of possibility.
As for going back a generation, one of the most useful things is to look at the witnesses to the baptisms of the children. They may be relatives.
The Agnes born in 1722 can be ruled out, as she would be 57 in 1779, too old to be a mother.
