After serving as a mistress to the King for just over two years, O'Murphy made a mistake that was common for many courtesans, that of trying to replace the official mistress. Around 1754, she unwisely tried to unseat the longtime royal favorite, Madame de Pompadour. This ill-judged move quickly resulted in O'Murphy's downfall at court; a marriage was arranged to Jacques Pelet de Beaufranchet, seigneur d'Ayat (born 5 March 1728), who took place on 27 November 1755 in Paris. From this union, the former royal mistress had two children: the first one, a daughter, Louise Charlotte Antoinette Françoise (born 30 October 1756 - died 6 February 1759), died in infancy. Jacques de Beaufranchet was killed in action on 5 November 1757, at the battle of Rossbach, seventeen days before the birth of their second child, a son, Louis Charles Antoine Pelet (born 22 November 1757 - died 2 July 1812), the later comte de Beaufranchet and General under the Republic.