Who is Lenore from Plain Kate and what is their importance?

Lenore is Drina's mother. She was killed during the skara rok because she was a witch. The people of Lov tried to burn her, but somehow she got away only to drown in the canal. This caused Lenore's spirit to become a rusalka, an evil river spirit. Linay learns how to free Lenore from this form by seeking revenge for her death. However, when Lenore returns to her human form, it is only for a brief time.