Excellent reasoning here by Dominique Ritchot, and I'm not biased either way if Francoise Grenier was Algonquin or not.
And despite the suggestion to the contrary, mitochondrial DNA **is** very conclusive here, because of the method of triangulation used by the French DNA Heritage Project. They have tested four female descendants from 3 different daughters of Francoise Grenier, and all four have the same European haplogroup (J2b1a1). This result would be highly unlikely if there had been an adoption or other "non-parental event" in any one of those four lines down to the descendants. If any NPEs are in any of these four all-female lines from Francoise Grenier down to these testers, then the chances of all still showing the same haplogroup are extremely remote.
DNA does not lie, and certainly a test as extensive as the above by the French DNA Heritage Project is about as certain as you can get. Francoise Grenier has a European background, not Native American. Absolutely case closed.