I'll say it: what the hell is Sansa doing? First, she reminds a borderline hostile Lord Glover of his obligation to rally behind the Starks, a poor decision that causes Jon to sigh and Lord Glover to refer to Robb Stark's dead wife as a "foreign whore." Then Sansa disses Davos snarkily to Jon's face after the Onion Knight had single-handedly won Lyanna Mormont over to their cause. Finally, Sansa schemes. Without telling Jon or anyone else of her plans, she fires off (quills out?) a letter, destination unknown, after being seemingly upset with Jon's insistence that they march on Winterfell as-is, with only 2,000 wildlings, 200 Hornwoods, 143 Mazins, and 62 Mormonts. No one puts Sansa in the corner.
So whom did she send the letter to, via Mormont raven? It can't be going to any of the Northern houses already mentioned, including Houses Glover, Mormont, Manderly, Mazin, Hornwood, and Cerwyn. It can't be the Blackfish, because Sansa has already dispatched Brienne to Riverrun to enlist her great uncle and his men in their fight. Did she send it to Littlefinger? Possibly -- but the letter was signed a bit too formally, not to mention that asking for his help would undermine everything she said to him during their showdown earlier this season.