This is first-person, stream-of-consciousness voice-over narration. 

This kind of narration helps us to get inside the head and relate more to the central character. It’s much like reading a novel written in the first-person. Here, the voice-over helps us to understand the subtext of the scene when Cady says she’s lost, but actually knows more than Aaron. Without the voice-over, we wouldn’t be fully privy to that irony.