In the book, it was some guy who worked for the mountain, torturing people. She stabbed him like a dozen times, punctuating each stab by asking him one of the questions he'd ask while torturing people. Even the Hound was probably thinking "THIS GIRL NEEDS COUNSELING. A LOT OF IT."
Dang, that sounds insane! Jaqen killed that guy at Harrenhall in Season 2 at her request. Can't wait for Season 4 already! Oh yeah, and life sucks for Sansa Stark, but what else is new? At least Joffrey's wedding approaches: