Side with Arya

Rounding the corner, you approach the group of women, who round on you being the newest addition to their argument.

"Apologies, Lady Stark, Sansa, I couldn't help but overhear. Arya was with me most of yesterday, and I left her with Old Nan in the evening, preparing for bed. She would not have had the time, or opportunity, to have away with your sewing kit Sansa," he threw a smirk at Arya surreptitiously, "although it does sound like something the little one would do."

Catelyn gives you an appraising look, whilst Sansa starts to angrily splutter from the intrusion.

"Enough." the Lady of Winterfell interjects, still look at you. The next few words seem to rankle as they come out, "thank you Jon. Sansa, Arya, return to your rooms. Sansa, I suggest you look more thoroughly for your belongings, and keep better care of them in the future. Arya, if I do find out you had anything to do with this, I will be displeased, and I will tell your Father. Jon, shouldn't you join the young men in the courtyard to train?"

The last was more of a command than a question, as Catelyn Stark stalked off, straight-backed and proper, down the corridor.