The big reveal on last night’s episode of Lost was that Claire’s friend is The Man In Black (who has assumed control of Locke’s body). There is, however, more to the story (as there usually is on Lost.
Claire was last seen with her father on the island, Christian Shepard (another of the Man In Black’s adopted personna’s). This was also during the time when he pretended to be Jacob in the cabin.
In addition, it’s clear now that Jacob was preventing babies being born on the island specifically because he wanted to prevent them being ‘claimed’ by the Man In Black.
Credit: E! Online