Maeve. Importantly, uninfected Maeve.
My idea on the different decision is Harry refusing to use Amoracchius against Lea to renege on his deal, and escaping some other way. Lea is unable to trade the Sword for the athame, and so it isn't given to her. The infection never spreads to the Winter Lady. (The athame is instead given to Ferrovax, which makes stuff way worse).
Harry brings her back across, Maeve is shown how much better Molly is at being the Winter Lady than she ever was, and suffers a change of heart. She takes over for Prime Winter Lady, and Molly drops her own Mantle on Halloween.