Warning: Some spoilers for this season of Game of Thrones ahead.
Sansa Stark has been rising in the Game of Thrones power rankings for weeks—seasons, really. Once a privileged young girl of Winterfell who didn't care to focus on much outside of herself, Sansa has become a true force in the Seven Kingdoms. She's my personal choice to sit on the Iron Throne when this saga wraps up in three weeks.
The most popular guesses as to who might take down the queen are her brothers, Jaime and Tyrion, and Arya. This is thanks to the prophecy from Maggy the Frog, which Cersei heard as a child. In the books it says, "And when your tears have drowned you, the valonqar shall wrap his hands about your pale white throat and choke the life from you.” Valonqar means "little brother," which at first glance would mean Tyrion. But it could apply to Jamie too, considering he's the younger twin. Notably, though, that specific part was left out in the show. And then, of course, Cersei sits high on Arya's kill list.
But it would be super cool if it was Sansa, especially since Arya just had a big moment in killing the Night King.
Don't forget that Maggy's prophesy also includes this bit: “Queen you shall be…until there comes another, younger and more beautiful, to cast you down and take all that you hold dear.” Sounds like Sansa, no?
So how might this all go down? The dagger that Arya gave to her older sister during the Battle of Winterfell plays a big part. "Stick 'em with the pointy end," Arya says, in a callback to the same advice Jon Snow gave to her in season one. While Sansa has never trained to be a physical fighter like Arya, she has learned a lot about politics and manipulation from Littlefinger and Cersei herself. The theory points out that, in season seven, Sansa admitted to "learning a lot" from Cersei.
"What if it’s actually the person she least suspects? It would be satisfying as hell to watch Sansa kill Cersei with Arya’s dagger," Avery Thompson writes for Hollywood Life. "Sansa learned so much from the Queen of the Seven Kingdoms. Cersei helped shape Sansa into the woman she is today. But just like Arya, Sansa harbors a hatred for Cersei. Cersei had a hand in having Sansa’s father, Ned, killed, which Sansa had to watch from just inches away. She helped keep Sansa in King’s Landing and away from her family for years."
The motive is definitely there—and thanks to the dagger from Arya, Sansa now has the means. But will she take her shot when the opportunity arises? I guess we'll just have to wait and see.