She thinks it is poetic justice that makes her choose his blade, but it is really the assurance of a swift and painless release.
...
Her father; she thinks of her father as she does it. He thinks of her mother as Valyrian steel whispers out of his chest, scraping his silver sigil.
"Cat..." a thready sound almost lost in the wind, the echo of an echo, as he falls. Instinctively, she catches him, the girl with eyes as blue as a distant river and hair as red as blood. He smiles faintly as the sight, gentle hands cradling him to the ground. As Littlefinger convulses weakly, breaths shallow, she holds the boy close and mourns for a boy of Riverrun, a boy whom she called Petyr.