PatLac, this is great, thank you. I think that the younger Christopheretta on the tree is probably my girl.
A few questions remain though. Firstly, how did she become a D'oiley? Secondly, why her name on Ancestry was originally Mary Gardiner?
In the post from ciderdrinker, John Gardiner's wife is Mary. In the Family Search tree it is Christopheretta. It seems there are two Mary/Christopheretta conundrums.
Nonetheless, I am sure I am now on the right track. Thanks again to ciderdrinker and PatLac.