With Jaime gone, Brienne's likely doubled down on her dedication to protecting Sansa, and that's a good thing because the Lady of Winterfell is in serious need of protection right now. Daenerys knows who sowed the seeds of her downfall, and the paper trail leads right back to Sansa. It would be shocking if the Dragon Queen didn't come for Sansa now that she's decimated King's Landing. Brienne is likely bracing for a battle, and while she's a dark horse in terms of candidates to take out Daenerys, having her add dragonslayer to her growing list of titles wouldn't be a bad way to wrap her story.