A very helpful contact has found a couple of relevant events.
It looks like Darnaty SMITH didn't live very long and was buried at North Bradley, Wilts on June 8th 1778.
However her parents may have baptised a daughter Eleanor at Wingfield, Wilts in June 1773.
This could be Eleanor, wife of William Draper, who would be my Darnaty's grandmother. The baptism mentions Bow Brickhill which is where Eleanor Draper died.
I'm still interested to hear from anyone who knows more about Mederick SMITH and his wife and their children.
Thanks