Catherine Turnbull and John Cook are on the same page in the marriage index Jul-Aug Sep 1866 West Derby Vol 8b page 870.
I would have expected her to be married as a Cooile not a Turnbull. note that in 1861 she had a daughter, Mary E.
There is an Alfred Cook born in Liverpool in the Jul-Aug-Sep quarter of 1867 vol. 8b page 51.
In 1881 Catherine is married and living in Rushen with Alfred, next door to Thomas and Margaret Turnbull and Harriet Cooile. She is a mariners wife.
Hariett is the daughter of Henry Cooil and Catherine Turnbull.