Thanatos said that only one sort of demigod can read the signs to the Doors of Death, well I think that would be, well, a dead demigod or a demigod that used to be dead, like Hazel, I don't really think it matters that she is a child of Pluto I think RR just made it like that to confuse us. I think she might see things that other people wouldn't see like the raven, for instance, it was very mysterious and I think there is more to it. I think a DoD might be found wherever a talking raven of something like that is(that sounded much more plausable in my head). But as always RR is completely unpredictable(curse him :D).