While folks may fault Sansa for not making smart decisions when she was younger, two highly-regarded characters give the redhead props on her growth since her bratty beginnings. When Tyrion comes to speak with her, the two commiserate over their annulled marriage and the disaster that was Joffrey's wedding ("It had its moments.") The two have a long and delicate history with one another — when Sansa was a prisoner of the Lannisters, Tyrion was the only one who could really protect her even before they were married. Now, Sansa is a grown woman and powerful in her own right, a fact which Tyrion compliments her on: "Many underestimated you. Most of them are dead now."
In return, Sansa opens Tyrion's eyes to his own naivete. Though the older man has been thought to be "one of the cleverest people" on the show, he's slipped in a lot of ways and his faith in Cersei is one of them. Being completely open with her former husband, Sansa points out how foolish he is for actually believing that Cersei would send Lannister bannermen to aid them in the Great Battle. She knows Cersei — maybe even better than Tyrion since the Queen often spoke to Sansa woman to woman — and she knows to never trust her.
On the other side of Winterfell, Arya and Jon have a reunion that shows exactly how far the Stark sisters have come. When Jon tries to reconnect with the younger sister he hasn't seen in years by using their frustration with Sansa as common ground and noting that she thinks she's smarter than everyone else, Arya rebuffs his comments.
"She's the smartest person I've ever met," she says, adding that Sansa is just defending their family. It's a beautiful moment that shows not only have the sisters found their way, but they've also come to see each others' strengths.