23 November is my best guess for Eleanor's birthday in 1241. There is no way that we can be certain about the date, but given that her father Ferdinand III was reunited with her mother in February of that year, she must have been born in late November in order to have been 49 (as her memorial arrangements indicate) at the date of her death. Eleanor was probably born somewhere in the Valladolid region, home to some of Spain's most wonderful medieval castles, including this one, the castle of Penafiel.
23 November was already a very important day in Eleanor's family - it was the birthday, in 1221, of her beloved brother Alfonso X, "The Learned", himself made Lord of Penafiel. Thus Alfonso was very possibly exactly 20 years Eleanor's senior.
It was also the date in 1248 when formal terms of capitulation were signed by the authorities of Seville, marking Ferdinand's acknowledged conquest of that wonderful city The date was almost certainly chosen deliberately to coincide with the already significant date for the Castilian royal family. When they entered the city the next month they would find astonishing beauties awaiting them, including the Giralda tower, which survives to this day.
Finally either on this day, or on 24 November, in 1273 Eleanor would give birth to her son Alphonso, named for his uncle and godfather. Alphonso was almost certainly Eleanor's favourite child, being almost the only one with whom she was able to spend much time throughout his childhood. At around this date in 1283 Eleanor and Edward made a special donation of alms to celebrate his birthday. At ten it was probably felt that he had safely naviagted the hazardous years of childhood. But the celebtrations came too soon. Alphonso never celebtrated another birthday, dying on 19 August of the next year.