The woman's body was found next to her car by the side of a river, said Pierre Soubelet, the representative of the Var department on the Mediterranean coast. The woman was understood to have been out with her daughter at the time.
"Her daughter has not been found. It is likely that the child has died," he said yesterday.
According to witnesses two more people had fallen into the river, he added.
Interior Minister Bernard Cazeneuve gave a toll of "one dead and three people missing" late yesterday.
Earlier this month, storms in southern France left six people dead, including a mother and her two small sons whose vehicle was swept away on a submerged bridge.