She was implicated in the Cellamare Conspiracy of Giulio Alberoni against Philippe II, Duke of Orléans, regent for Louis XV of France, and was sent in 1718 to the Bastille, where she remained for two years. Even here, however, she made conquests, though she was far from beautiful. Her own account of her love for her fellow prisoner, the chevalier de Ménil, and of the passion of the chevalier de Maisonrouge, her gaoler, for her, is justly famous. She returned on her liberation to the service of the duchess, who showed no gratitude for the devotion, approaching the heroic, that Mlle Delaunay had shown in her cause. She received no promotion and still had to fulfill the wearisome duties of a waiting-maid. She refused, it is said, André Dacier, the widower of a wife more famous than himself, and, in 1735, being then more than fifty, married the Baron de Staal. Her dissatisfaction with her position had become so evident that the duchess, afraid of losing her services, arranged the marriage to give Mlle Delaunay rank sufficient to allow of her promotion to be on an equality with the ladies of the court. On this footing she remained a member of the household. It was at this time that she became the friend and correspondent of Mme du Deffand. She died at Gennevilliers. Her "Mémoires" appeared about five years later, and have often been reprinted, both separately and in collections of the memoirs of the 17th and 18th centuries, to both of which the author belonged both in style and character. She has much of the frankness and seductive verve of Mme de Sévigné and her contemporaries, but more than a little alloyed with the sensibility of a later time. It may be doubted whether she does not somewhat exaggerate the discomforts of her position and her sense of them. In her lack of illusions, she was a child of the 18th century. Sainte-Beuve says that the most fit time for the reading of the "Mémoires" is the late autumn, under the trees of November, but her book is an extremely amusing one to read, as well as not a little instructive. The humours of the court of Sceaux are depicted as hardly any other society of the kind has ever been.