Eleanor survived Richard and lived well into the reign of her youngest son, King John. In 1199, under the terms of a truce between King Philip II and King John, it was agreed that Philip's 12-year-old heir-apparent Louis would be married to one of John's nieces, daughters of his sister Eleanor of England, queen of Castile. John instructed his mother to travel to Castile to select one of the princesses. Now 77, Eleanor set out from Poitiers. Just outside Poitiers she was ambushed and held captive by Hugh IX of Lusignan, whose lands had been sold to Henry II by his forebears. Eleanor secured her freedom by agreeing to his demands. She continued south, crossed the Pyrenees, and traveled through the kingdoms of Navarre and Castile, arriving in Castile before the end of January 1200.
King Alfonso VIII and Eleanor's daughter, Queen Eleanor of Castile, had two remaining unmarried daughters, Urraca and Blanche. Eleanor selected the younger daughter, Blanche. She stayed for two months at the Castilian court, then late in March journeyed with granddaughter Blanche back across the Pyrenees. She celebrated Easter in Bordeaux, where the famous warrior Mercadier came to her court. It was decided that he would escort the queen and princess north. "On the second day in Easter week, he was slain in the city by a man-at-arms in the service of Brandin," a rival mercenary captain. This tragedy was too much for the elderly queen, who was fatigued and unable to continue to Normandy. She and Blanche rode in easy stages to the valley of the Loire, and she entrusted Blanche to the archbishop of Bordeaux, who took over as her escort. The exhausted Eleanor went to Fontevraud, where she remained. In early summer, Eleanor was ill, and John visited her at Fontevraud.
Eleanor was again unwell in early 1201. When war broke out between John and Philip, Eleanor declared her support for John and set out from Fontevraud to her capital Poitiers to prevent her grandson Arthur I, Duke of Brittany, posthumous son of Eleanor's son Geoffrey and John's rival for the English throne, from taking control. Arthur learned of her whereabouts and besieged her in the castle of Mirebeau. As soon as John heard of this, he marched south, overcame the besiegers, and captured the 15-year-old Arthur, and probably his sister Eleanor, Fair Maid of Brittany, whom Eleanor had raised with Richard. Eleanor then returned to Fontevraud where she took the veil as a nun.
Eleanor died in 1204 and was entombed in Fontevraud Abbey next to her husband Henry and her son Richard. Her tomb effigy shows her reading a Bible and is decorated with magnificent jewelry. By the time of her death she had outlived all of her children except for King John of England and Queen Eleanor of Castile.