Isabelle was born in 1212, the youngest daughter of Amaury I, Sire de Craon and Jeanne des Roches (c.1195- 28 September 1238).
[1] She had a younger brother, Maurice IV, Sire de Craon (1213–1250), who married Isabella of Lusignan,[1] a half-sister of King Henry III of England by whom he had three children.
She had an elder sister, Jeanne who was bethrothed to the three-year-old Arthur of Brittany in 1223.
Her maternal grandparents were Guillaume des Roches, Seneschal of Anjou and Marguerite de Sablé.
Being the husband of Jeanne, eldest daughter of Guillaume des Roches, the hereditary seneschalship of Anjou and the vast Sablé barony passed to Isabelle's father upon the death of her maternal grandfather on 15 July 1222.