WOJ confirms Mother Winter is, she's Baba Yaga
WOJ: if the Ladies become the Queen, what happens to the Mothers at that point? The thing is that the Mothers are kind of the foundation. So, it’s not so much what happens to them because the little mantles changed. It’s what happens to the little mantles if the big mantles change. So, if someone whacks the being that is, for all intents and purposes, Baba Yaga, and then Mab succeeds, then Mab becomes the new Baba Yaga, and Molly gets drawn up to Mab, and they have to find someone else to become the new Lady. But on the other hand, the Mothers are extremely powerful beings (continued in the cosmology/mantle sub-section)