#i do wish grrm had taken this just a lil further

[gendrie]

"Lord Stark asked for his sisters and his father's sword as well," Ser Cleos reminded him. "As you say. And his sisters?" Tyrion glanced toward Sansa, and felt a stab of pity as he said, "Until such time as he frees my brother Jaime, unharmed, they shall remain here as hostages. How well they are treated depends on him." And if the gods are good, Bywater will find Arya alive, before Robb learns she's gone missing. (Tyrion, ACOK)

on my last reread this really stuck out to me. at the end of agot sansa "forgets" to ask what happened to arya. when she hears the crown demand arya present herself (or else) sansa just assumes that her little sister got out of the city and returned safe to winterfell. an assumption which carries over to the beginning of clash. this is classic sansa. i don't think she wants to consider that arya is dead. for obvious reasons, but also bc sansa herself would share the blame on account of the fact she told cersei about ned's plans and, more to the point, arya's location that morning. which is why meryn and co. knew where to find arya in order to arrest her (and failed only bc of syrio's sacrifice)

but then sansa is in the throne room when cleos asks about arya being returned to robb which means the starks dont have her. tyrion responds that the lannisters arent giving either girl back. he clearly implies they have arya. its a lie, but sansa's theory about arya's safe return is falling apart

Meekly, Sansa dropped her eyes and retreated back inside. She realized suddenly why this place seemed so familiar. They've put me in Arya's old bedchamber, from when Father was the Hand of the King. All her things are gone and the furnishings have been moved around, but it's the same . . . (Sansa, ACOK)

later, sansa is brought to the tower of the hand where tyrion now resides. they place her in arya's former bedroom but she is not there nor are her things. sansa's thoughts trail off as she looks around. she doesn't think about it anymore. i don't think sansa likes where this is going so she doesnt investigate further by inquiring to tyrion about her sisters whereabouts. she could, but she doesnt. its peak avoidance.

"Joffrey will show you no such devotion, I fear. You could thank your sister for that, if she weren't dead. He's never been able to forget that day on the Trident when you saw her shame him, so he shames you in turn. You're stronger than you seem, though. I expect you'll survive a bit of humiliation. I did. You may never love the king, but you'll love his children." (Sansa, ACOK)

its cersei who confidently and casually informs sansa that arya is dead. the logical conclusion here would be that the lannisters captured arya (as they were actively trying to do) and killed her.

again, sansa has no reaction to this revelation. i don't actually think this is apathy or even that sansa cant react bc shes a hostage - or at least not entirely in the case of the latter. for comparison: arya finds out bran and rickon were murdered when serving roose and she cant react either, but we get her grief internally. for sansa its the guilt imo. deep down sansa realizes that she betrayed arya and, apparently, got her little sister killed. that is a very heavy thing to bear. sansa very rarely likes to assume guilt for her actions so it gets buried.