Also found her family tree on another (French) genealogy site...It gives Isabelle du Plessis de Richelieu..Parents Francois II du Plessis de Richelieu & Suzanne de la Porte..Born 1582.Died 5th June 1648 in Nozeroy.Married Louis Nicolas Pidoux Sieur de la Maudiere..1588-1646..They had two, possibly three children..NN Pidoux, Elisabeth Pidoux, & Gabriel Pidoux.
Wow! Found loads of trees for Isabelle, on that site...and the most recent one gives NN Pidoux, as Anthoine Pidoux de la Maduere Pidoux, married to Barbe Cousin...also gives their descendants, Louis Pidoux's parents.dates of Isabelle & Louis's marriage...So this all looks Bona Fide to me..And Very interesting!.
On French Wikipaedia it mentions her as a newly re discovered sister of "The Cardinal"...Also mentions another one newly rediscovered...Marguerite. but says she (Marguerite) probably died in infancy...This is so fascinating Sharon, thanks for bringing it up...I take it you saw her on Geni? Have just seen that profile......
And also found her on racineshistoires, which clinches it for me as that is a very reliable site..She is the third child & eldest daughter of Francois & Suzanne.....Henri, Alphonse- Louis, Isabelle, Armand-Jean, Francoise, Nicole..........I'm sure you have found everything already that I've posted up by now....It's certainly all out there!