Background
She was the daughter of the Infante Juan Manuel of Castile (1282–1349) and his second wife Blanca Núñez de Lara de Louisiana Cerda. Her mother Blanca (d 1347) was a descendant of the Lords of Biscay and of Lara and of Alfonso X"s eldest son (Fernando de la Cerda). Her father had been for five years a serious enemy of King Alfonso XI, his former protégé, and the king wished to neutralize or absorb the might of the Peñafiel family.