Marie is probably sister of Cecile and Felix. They look exactly like each other.
I sometimes wonder about a picture of "Marie Winckler" with Julia Restoin Roitfeld, Charlotte Casiraghi, and Eugenie Niarchos at a Valentino party. The caption definitely referred to "Marie Winckler" but of course everyone assumed it must be Cecile and that the caption was wrong. Now I wonder because maybe it really was her sister Marie and because they look so much alike, no one could tell the difference. Maybe they are even identical twin sisters.
Sometimes when it seems like Cecile, maybe it's her twin, who knows?