Just because she's petty doesn't mean Sansa isn't still a capable leader of her people. When Jon and Tyrion rile up the Northern lords with their talk of joining hands for survival and bonding with enemies, Sansa asks the most rational question: How are they even going to feed all of the soldiers in the camp AND two full-grown dragons?
It's important to remember that, in the season before, Daenerys destroyed all the food travelling to Kings Landing from Highgarden, which means that she most likely came to Winterfell with little to no resources to keep her soldiers from starving. Which means that, as the lady of the house, it falls on Sansa to provide for everyone. And it may not seem like much to viewers, but soldiers who don't get fed aren't likely to put their lives on the line for the people starving them. Nor will they survive very long themselves.
No one answers Sansa's question but Daenerys pointedly says that dragons eat "whatever they want" — which is kind of the worst thing to say in a room filled with people already wary of your bloodthirsty children. Daenerys loves a power move, but her comment proves that she has no control over her animals and they will probably be eating up a huge amount of the food already meant for the people of Winterfell. Whew, the shortsightedness of it all.