Shirl is of royal blood because the Ravenlocks used to rule the Callahorn until the Buckhannahs came to power. She believes that Balinor Buckhannah's younger brother Palance intends to ask for her hand in marriage. The mystic Stenmin drugs and kidnaps her, to be used as blackmail to force Palance to open the gates of Tyrsis to the Northland army.
Shirl is accidentally rescued by Menion Leah, who mistakes her for Shea Ohmsford. She stays by Menion's side as he convinces the Council of Kern to evacuate to Tyrsis, and she later joins Menion and his companions on their journey to defend Tyrsis against the advancing armies of the Warlock Lord.
During this time, Shirl consoles Menion over his guilt over not being able to protect Shea. Eventually, Menion and Shirl confess their love to each other and some time after the war they marry.
Terry Brook's annotations in his 2012 edition refers to love as the virtue that drives the narrative of The Sword of Shannara and that Menion and Shirl represent male/female love. In the story, Shirl displays fidelity at its highest level.
Shirl is a direct descendent of Kinson Ravenlock and Mareth, who traveled with Bremen to save the Four Lands during the Second War of the Races. She is the great-grandmother of Rone Leah, connecting the bloodline of the Ravenlocks to the House of Leah and eventually to the House of Shannara. (Rone had children with Brin Ohmsford, and centuries later Railing Ohmsford and Mirai Leah had children together as well.)