18 Game of Thrones Season 7 Theories to Read Until the Show Returns

Now-queen Cersei already blames Sansa for her beloved son Joffrey's death, so when she discovers that Sansa has retaken the Stark family home and proclaimed Jon "King in the North," she won't take kindly to it. She'll definitely have a violent response, either via Littlefinger as a proxy or by sending her own armies to fight the northern bannermen.