Interesting discussion. One area where I do have a bit of a disagreement is that the protagonist is unambiguously coded as a vampire. She does drink blood and avoid mirrors, but she's covered in fur like a werewolf*, and later haunts the house like a ghost. To me, Atwood put our myths into a blender and recast this girl as a kind of universal monster, a representation that society can project it's fears onto anyone different.
While the character in the book can come across as cold, disturbing, and in some ways subhuman, it's clear that she's that way in large part because of how she's been treated. I don't even want to think about the psychology of a family that would ask a child to lie down and play dead in its own coffin.
* Let us not forget that werecats are also a traditional type of monster. Someday I need to commission an episode on Val Lewton's "Cat People".