Is Molly's apartment one of the ways she stays human?
Molly Carpenter owns that apartment as payment from the Svartalves for services on her part. The Svartalves are not fae and don't play by fae rules or definitions of identity. The Winter Lady may enter the apartment as long as she has good intentions toward the owner. But, Molly Carpenter =/= The Winter Lady under fae rules. Just as Kringle =/= Vadderung.
We've never seen Molly in her apartment since she became the Winter Lady. Harry dropped her off there in Peace Talks, but other than that it's only mentioned that she breezed through on brief stops to pet Mouse, play with Maggie and share some sunny chat. (Which sounds like what a teen/twentysomething would do to not make her family worry.)
Perhaps that's one of the reasons that Mab keeps Molly so busy? So that she won't have an opportunity to retreat to her apartment.
After Harry made a bargain with her, she had the excuse to go there to complete the obligation of the bargain, then she was back to the marathon of building up Winter's forces.
So, when she's inside her apartment does the Winter Lady take a back seat and the mortal Molly get to come out to play?
