Zanica is an Aes Sedai. She has remained loyal to the White Tower during the split. Her Ajah is not currently known, but she is not Blue Ajah because she is a loyalist, and also she is not Red Ajah as she has a Warder.
She is also secretly part of the Black Ajah.
Egwene al'Vere has some lessons with her.
Zanica is listed as a member of the Black Ajah in Verin Mathwin's book.