Béatrix was born in 1075. Béatrix's father was Gaultier D'ath and her mother was Ada De Montdidier. Her maternal grandparents were Hilduin IV De Montdidier and Alix Ou Adèle De Roucy. She had a brother and two sisters, named ?, ? and Ade. She was the second oldest of the four children. She had a half-brother named Guy. She died before 1136.