Former dancer who married morganatically the duc de Deux-Ponts (1757). Ennobled by King Louis XV as the comtesse de Forbach (1757), under which name she became a friend and correspondent of Franklin. Friend also of Grimm, Diderot, and Rousseau.

Her nephew, Fontevieux, fought in the American Revolution. Her two sons, Christian and William, barred from dynamic succession, also fought in America with their regiment of Deux-Ponts and distinguished themselves at Yorktown.

The duchesse maintained an interest in dance, music, and the theater throughout her life, and created an amateur theater and small orchestra at the Court of Deux-Ponts.

Alternate form of the name: Forbach, Marianne Gamache.