I highly doubt she knows how his wife is, and I don't think we are expected to believe she knows. I think the point of her saying that was to calm Jack down and we are to take nothing more than that away from it.
I'll agree with that.
However, the episode showed that the Others had/have very significant contact with the world (Stephen King novel?). So who knows what they can know.
Of course, this was the first episode I've ever watched.