Philippa was the daughter of Sir Gilles de Roet, who was a knight of Hainault and accompanied Queen Philippa to England. He later became the Guienne King of Arms. There is no history of her mother, but it is thought that Philippa had two sisters and a brother: Katherine, Elizabeth, and Walter. Her father went to serve the queen's sister, Marguerite, who was the empress of Germany and the three younger children – Walter, Philippa and Katherine – were left in the care of Queen Philippa.