Do you think she is still the girl she was in Season 1? Have you been ignoring her behaviour the past few episodes? Or in Spoils of War alone? She has thought of nothing but the North throughout this season.
Thinking ahead and preparing for not only the war that is to come, but the long Winter and how the Northerners with weather it.
When she questions Jon? It’s because she believes him to be the King he is, and wants him to live long enough to rule it, unlike Robb. He is the first family she has seen in years, she doesn’t want him to leave Winterfell, or her.
Those saying she is power hungry? She did not offer Bran Jon’s title, she offered him hers. Because he has every birthright to be the Lord of Winterfell, but he isn’t their King.
And when her sister is finally home. She acknowledges that Jon loves Arya more than words can describe. And she knows how deeply Arya cared for Jon, look at the smile on this precious muffins face at that prospect of seeing her favourite sibling. Sansa made that genuine smile happen.
Sansa has offered nothing but wise counsel based on her knowledge she has obtained through her toxic situation in King’s Landing. She is making the most of what she has learned in the Capital to ensure the security of her people and family. She can even conceal her emotions exceedingly well.
She knows what needs to be done, and she knows how people think. The look she gives Lyanna, isn’t only an impressed and satisfied one. But a knowing one. She knows every able bodied person must be provided for and prepared for the Long Night.
That’s why I think, while watching Brienne and Arya spar, she gives that look. It’s not one of jealousy like so many people are saying. It’s one of fear. She hides it behind her trained facade, but she see’s Arya fighting with such skill, and she knows, especially with that Valyrian steel dagger, Arya will be on the front lines with Jon. She doesn’t want to lose her family again.