1

She used to be stupid.
"A great many people underestimated you," Tyrion says, the first time he sees her. "Many of them are dead now."
It is meant to be a comfort, but it isn't, because there are too many men in the castle for her to feed, and the dead have come walking, and her brother has bent the knee to the dragon queen mere months after they gave him a crown, but at the very least, no one is underestimating her anymore.
or
the one where they fight off dead men and Tyrion and Sansa fall in love along the way. Part 3 of the series, but can be read as a stand alone

Everything you recognize was created by HBO or George R. R. Martin. This is a fan fiction