Who is Mama Yaya from I, Tituba, Black Witch of Salem and what is their importance?

The elderly, eccentric Mama Yaya adopts Tituba after the deaths of her parents and teaches her the ways of nature, most importantly ways of healing and how to communicate with the dead. In many ways, she mentors Tituba, both as a living being and as a spirit - she, like Abena and Yao, manifests to Tituba in times of need and/or stress. Yaya's presence is sometimes irritating to Tituba, in that she (Yaya) doesn't always give the answers and/or guidance Tituba thinks she wants. Nevertheless, her presence and support is an invaluable refuge to Tituba in times of trial, and even at the moment of her (Tituba's) death.