You're right that, as I understand it, she's not essential. It's the Phinney side -- Isaac is the fifth generation from Mayflower passenger Thomas Rogers. So the Society project ends with his birth (unless someone else has brought it further - that inquiry is pending with them, but I'm not optimistic).
The big problem is that Isaac and Anna moved to Nova Scotia, so I'm working on that now. There's a secondary source on the Phinneys that brings them down to the couple who returned to Boston c. 1882 (I've got almost everything from there down to my wife), and which is cited in the Five Generations book, but which I assume is not alone sufficient.
A work in progress, as they say.