Daughter of Lord Reynard Reyne of Castamere and sister to Roger the Red Lion and to the second Reynard who would lead his line to its end. She was carried to Casterly Rock as a girl to wed Ser Tion Lannister, second son of Lord Gerold the Golden and twin to Tywald, in a match meant to bind her brothers closer to the Rock; Tion gave her no children before he fell at the Battle of Wendwater Bridge in the Fourth Blackfyre Rebellion in 236 AC, and his widow was left to a long and corroding ambition that turned at once upon his younger brother Tytos. When Tytos failed of his manhood in her presence and went to his lady wife Jeyne weeping of it, the matter was carried to Lord Gerold; he wedded Ellyn off swiftly to the aging Lord Walderan Tarbeck of Tarbeck Hall, and so set the grievance.
By Walderan she bore three children, and through her years at Tarbeck Hall she pressed her brothers and her husband alike toward the seat she had been denied. When in 261 AC her son Tion Tarbeck rose in revolt against the lordship of Tytos, and her brothers raised Castamere's banners in support, Ellyn was the council that drove them; her son was struck down at Tarbeck Hall by the answering host of young Tywin Lannister, and the keep itself thrown down upon her head as the song The Rains of Castamere was first being sung in his ranks.