She was born to Charles Boucher d'Orsay, seigneur d'Orsay and Marguerite Bourlon and married Henri de Mornay, marquis de Montchevreuil (1623–1706) in 1653.
In 1679, she was appointed to the Household of the new Dauphine Maria Anna Victoria of Bavaria: she was appointed to the post of governess of the Dauphines maids-of-honour, serving under the Première dame d'honneur Anne de Richelieu and the Dame d'atour Madeleine de Laval-Bois-Dauphin.
[1] She was a friend and confidante of Madame de Maintenon, and had some influence at court.
Elizabeth Charlotte, Madame Palatine claimed in her letters that Madame de Maintenon did not wish the Dauphine to play any great role at court, slandered her against the king and bribed Barbara Bessola to isolate her.
Elizabeth Charlotte claimed that Marguerite de Montchevreuil had been engaged by Maintenon to estrange the Dauphine and her spouse, quote: Elizabeth Charlotte also claimed that the Dauphin did not mourn his spouse when she died, "old Montchevreuil had told him so many lies of his wife that he could not love her.