Zombies are real.

Zombies were a part of Haitian voodoo culture. If you pissed off your family or the leadership circle, they would take you to a sorceror and have him turn you into a zombie. Paralyzing toxins would be administered to subdue breathing and heartbeat, making the victim appear dead. Then they are exhumed and revived, never the same as they are permanently brain damaged from oxygen depravation and most likely have other nervous system damage, etc. They then are forced to be the sorceror's slave. If we were to say it's okay for them to be raped because they aren't really alive, how hideous would that be?

In the case of the movie, she appears to be a mental patient who can't die. Drugging is a possible explanation, but mental illness is another. The distinct point I want to make here, is she isn't "a corpse" and this is the type of desensitization I think the movie is trying to expose. The debate of "but she's a zombie, so is it the same?" in itself is a commentary about the horror of humanity.