OMG... Does that mean that the "book" she read wasn't a book? That was her trauma manifesting itself, making her believe the memories she has, and everything she knows came from a book?
It would make sense that she would know certain things, like Jeanette being a product of black magic, but not others, such as Jeanette's powers... Jeanette is acting like an anesthetic, stabilizing Claude with her presence because she want to be loved... that means that all those who love Jeanette possibly do (partially) because of her magic...
Claude probably did use black magic to bring back Athy's mother, and without Athy in his life during those first few years, the black magic started consuming him, and that's why he liked Jeanette in the first novel: she got him feeling better with her own black magic...