Only Danielle seems to know most of the secrets of the island. She knows about the island from a territorial perspective - she knows how large it is, where the dangerous areas are, what kinds of animals are loose and where they gather. She knows where the signal originates and where the 'others' are (even if she's never seen them). She knows where her ship is (or what's left of it). She knows about the Black Rock, the source of electricity on the island...etc etc
Some fans think she will be killed of at seasons end, but others want her to stick around and maybe pop in very 4th or 5th episode to drop a clue or two then vanish back into the jungle.
