Lysa Arryn is Jon Arryn’s widow; she’s Catelyn and Edmure’s sister. She sends a message to Catelyn early in the novel saying that she suspects the Lannisters killed Jon Arryn. Later in the novel, Lysa is portrayed as mentally unstable, and Catelyn becomes frustrated when Lysa grants Tyrion a trial by combat, a decision that ultimately leads to Tyrion’s freedom.