In the West the Lhiannan have their blood magic: Ogham. In the background of Baba Yaga she was a sorcerer before the Embrace. I think it's possible she created her personal magic with her knowledge. Perhaps her magic is similar to the Koldunic Sorcery, but with her power, i think could not be the case. The magic of Baba Yaga seems founded in pacts with spirits of the nature and the Wyrm (The Zmei and Koshchei). Perhaps Kupala is not the spiritual mentor of Baba Yaga, i think in another type of spirit...or demon.