DISCLAIMER: Sadly, I am only a fan, playing homage to a good series.
A/N: This was written based off of Season 6 of Game of Thrones, but uses characters/plots from the books.
Dacey and Mother and a whole horde of soldiers had answered the call of Robb Stark to avenge his father.
Neither of them came back, even though some of the soldiers did, but her maester swears the strange letter in the odd hand that came from Greywater Watch was from her mother.
Alysanne went away next. She had rudely told her maester that she was not going to stand idly by and watch that fucking Greyjoy turncloak destroy the North and then she took a substantial force of their army in the direction of the Iron Islands. Lyanna hasn't heard from her or her army, either, and makes up stories to tell her niece and nephew whenever they ask where their mother is.
After that letter from Greywater Watch arrived, Lyra and Jorelle disappeared. Lyanna's not as concerned as she probably should be, considering her sisters had disappeared in the middle of the night with no note, but that's only because no one seems to be looking for them, and she's too scared to bring it up to the staff- her staff, because that's what they are now, isn't it? She's now the Lady of Bear Island, quite possibly the only one with the Mormont name still alive, considering Uncle Jeor died and cousin Jorah and his wife disappeared when she was still a little girl that would dance with her father while she stood on his toes.
So the maester takes her under his wing and helps her learn how to not only run the household, but Bear Island itself. She sends letters and prepares for winter and makes sure the soldiers are prepared to face any threat- because Mother and Uncle Jeor would be damned if she didn't listen to the Night's Watch about threats facing the realm, facing the North, even if they were likely safer on Bear Island than anywhere else.
She questions every decision she makes, and almost doesn't send that letter to Stannis Baratheon, the one she feels Dacey would've sent had it been her choice- the only reason she does is because Rickmand Snow dares her to. When Lady Stark and the Lord Commander and Lord Seaworth arrive, the only reason she does it is because her mother would've, and Uncle Jeor would've made damn sure the Night's Watch had help turning back the monsters she'd overheard him and Mother talking about one time after Father had died.
Then when she stands up in the Great Hall and declares Jon Snow her King in the North, she knows it's what Alysanne would've done. Alysanne wouldn't have cared if Sansa or Jon was in charge, because Alysanne was-is-was-is- the last to care about whether or not she was-is-was-is- ruled by a woman or a bastard, but Alysanne would've known to pick the one who had proved more about themself to the people of the North. Sansa was nice, was strong, was passionate, and would be a great lady of the North, but Jon was a proven leader who could command armies and make men of the North and wildlings fight side by side… with only mild opposition, and even then, he could deal with that opposition like, well, like a king. She didn't regret her decision.
She may be small, but she is proud. The Mormonts stand at Bear Island, and there they will always stand.