How did you miss that? She cut Littlefingers throat with it last year. Bran gave it to her in the godswood.
Plus the library scene which most normal people think was brilliant, Was put in specifically to break up the dog pile after dog pile battle fatigue that sets in when watching super extended battle episodes with nothing but spear stabs, sword and battle axe hacking and arriw shooting. It was brilliant to break up that monotonous "flow" like they did, and reaplace it in a quiet Hitchcock like suspense filled atmosphere..I loved it.