I wondered the same thing!
1) I figured that after the Battle of the Bastards, the winning team either killed or imprisoned any of Ramsey's soldiers at Winterfell that refused to accept the new leadership. And the soldiers probably were smart enough to join the new Stark army.
2) Did Arya tell the Frey women to release Edmure from the dungeon? Probably the daughter that he married would -- particularly if Jaime was telling the truth about Edmure having fathered a son with her. Would any of the other women have done that on their own? They were in Riverrun, right? Would the women want to continue the Frey family behavior and teach the little Walder sons, which Arya didn't kill, to take revenge on the Starks? Would they run home to The Twins? Or were they just happy to be rid of old Walder? (like much of the rest of Westeros).
D&D do a poor job of following up on things like this. Other examples include the Reeds. Just dropping Meera after all she did for Bran. She was important in the story; doubly so, since her father knows what happened at the Tower of Joy.