I took it as they were presenting that Sansa may try and do Arya something. Littlefinger said to Sansa that Brienne is pledged to protect BOTH stark daughters so the same way Brienne would protect Sansa from Arya, Brienne would protect Arya from Sansa (or anyone else). Arya has Sansa shook so it would be easier for Sansa to scheme on Arya without Brienne in the way - that's why she was in her room. But Little Finger is doing what he does and subliminally planted the seed for that - what remains to be seen is if Sansa was up on game and flips it on him.Arya just making sure she's so far upside Sansa's head that she does not entertain any funny shyt. That whole face shyt means Sansa is not going to do anything slick in fear Arya has taken someone's face and might be finessing her, she might even stop consoling in LF as a result. What I did not get is LF telling Sansa to use Brienne and then Sansa sending her down south.