It has to do with the fact that this book is, at its core, about the question of just what it takes to unmake a confident young woman.
And the answer ultimately is:
a) quite a lot
and that
b) this nonetheless happens in our world all the time
Because ultimately, so much of what happens in this book with magic–of the ways in which our protagonist is undermined–also happens in our world without magic, as even the protagonist acknowledges. Magic often being metaphor, and all that.
And of course that makes for a pretty troubling story, one that, when well-handled (as this one was) lingers and demands one keep thinking about it.