He either laughed because what she said is funny or because it's a handy defense mechanism. It's not particularly funny, having daddy issues so she is leaning toward the latter. Her hunch is rewarded with what he says next. For a moment she feels she needs to debate him on his statement that it couldn't be helped but for some reason she doesn't feel like getting into it. So instead she watches him smoke his cigarette and shrug while she remains rather passive with not much to add to her observations.