Baba Yaga is an interesting character, and one that featured in stories throughout my childhood. Recently she's become something more to me, there is a calling that I'm not sure I want to answer, the things in those stories are not baseless. She is at times helpful and even benevolent, but more often than not Baba Yaga is the antagonist, she will kill you and eat you(possibly not in that order). And yet there is something else..
In all the stories I have read about her, she causes in one way or another necessary change. This is often unpleasant but it's still needed. In the story "Baba Yaga" the children are directed twice to see Baba Yaga, first by the wicked stepmother, then by their own grandmother. The children learn some lessons and Baba Yaga frequently threatens to eat them, Eventually they escape and run home to tell their father the story, the stepmother gets sent packing and things end up peachy.
This story would not work without Baba Yaga, she is the cause of change, the reason the stepmother is gone. Something similar happens in another story called "Vasilisa the Beautiful"
Anyway, onto something more squishy
Baba Yaga, as we know her, is a more recent character than Slavic Gods we know of such as Perun or Veles. I read in "The Encyclopedia of Russian and Slavic Myth and Legend" of the possibility that she has her roots in the Goddess Marzana(or Marena depending on the area). I can definitely see some similarities here. Marzana is a goddess of winter and death, in some cases also a sorceress. I'm not entirely sure of this squishyness, sure I can see some cross over but I just feel no connection for Marzana at this point.
Other sources see Baba Yaga as a protector of liminal spaces, specifically keeping things in or out of the spaces. She is also the Witch.
There is a myth I have come across a few times, though I cannot vouch for it's authenticity, it interests me somewhat. It's the myth of how witches came to exist.
If this is the story of the origin of witches, it makes sense to me of who the woman in the story is. I see Baba Yaga as the first Witch(which also pokes holes in my squishiness above). The associations with Veles also make sense to me, though I think that will be another post.