Dagneau was born in Sorel in 1689. She married Louis Maray de la Chauvignerie in Montreal, an officer in the troops of the Navy, an interpreter and a fur trader. On the death of her husband in 1725, Dagneau inherited his business. She held an enviable position in Montreal society.
Over the years, Dagneau learned Indigenous languages from her husband and his customers. Through her relationships with the major merchants in Montreal and the Indigenous peoples of the region, she conducted both legal trade and undoubtedly, smuggling. Dagneau didn't hesitate to denounce her competitors to the authorities.