I think she meant the 3 that Arya named to be killed. That Arya is responsible for their deaths and that if not meet again personally she will be judged by the Lord of Light.

Also as for all the so called spoilers, i haven't seen anything that i can count as such. I came to the same conclusions that Q pointed out. Sansa will not be doing anything of worth. She is simply a pawn to be played with. And she's powerless to prevent that. Even after getting married to anyone of power, all the once toying with her will still be of higher standings. Catelyn put herself in a position where she will be unable to do anything at all except advise. Until this war is over she will be able to do nothing. Can't see how pointing that out is spoilers.