I say four months because she's been on the island more two months. I guess it's really only three months, isn't it? It still goes to show that Claire was there for less time than the "dangerous" period of three months.
I really don't think they just wanted Aaron. If they did, they would have come back for him, right? ESPECIALLY when Danielle took Aaron and set up the black smoke.
I think Alex was mistaken when she said they were going to kill her. She knows that most women who go in there die, but she doesn't know why (only 16... I don't think Ben has explained everything perfectly well to her). Or, alternatively, she knows that Claire was going to get a C-section.
Really, if you grow up knowing that pregnant ladies die, what would you be saying?