Libby is an Other... that's why she was in the psycho ward with Hurley. But she looked wasted, which could have been medicine, but likely was an act.

Hurley could be the key to this whole thing, as others have speculated, and that would be why Libby LIKES him... b/c he's some kind of HERO to the Others!

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PIZZA?!?! Now that's what I call a TACO!!!