Who is Marie from A Distant Mirror: The Calamitous 14th Century and what is their importance?

Marie is Enguerrand and Isabella's oldest daughter. Marie is the heiress to the Coucy estate, and her husband, Henri de Bar, dies while still a young man. The death of her husband, which was preceded by the death of her father, leaves the estate in chaos, as Marie's stepmother decides to fight her for the estate. Marie is a direct ancestor of Henry IV.