I too am descended from Humphrey de Bohun 4th Earl of Hereford, and Elizabeth of Rhuddlan (Plantagenet). Elizabeth wasn't the eldest daughter of King Edward I by any means. Most of her sisters died before she was born, except three, Joan of Acre, Margaret who married John II Duke of Brabant, and Mary who died in 1333 'a nun'. Elizabeth had a strong sibling relationship with her brother Edward, later to be the ill-fated King Edward II. Elizabeth died in childbirth in 1316.