Recall the meeting at the National Tattler office (shown at left) at which Graham, Crawford, and Dr. Bloom work with Freddy Lounds to come up with details for a news story, which will hopefully draw the Tooth Fairy into a trap. During the meeting, Will at one point offers the idea that the killer may have had sex with his mother. This statement has, in fact, been placed in the movie as a hint that Molly and Kevin have been having incest.
Above left and right: Consistent with the idea that Kevin and Molly have been having incest, is that about midway through the film, Kevin is in his mother's bedroom in Captiva (to notify her of noise outside the house, perhaps from an intruder), and he doesn't appear to be uncomfortable or hesitant, suggesting that he is used to being in the room.
This incest between Molly and her son is the reason Molly has been trying to hide from Will that she is Kevin's natural mom - she's worried that one day, Kevin will mention to Will (and/or someone else) that there has been sex between her and himself. The reason Molly has 'let her hair go', i.e., has stopped curling it, by the time of the dock conversation at the Graham's new location (as indicated in part 46), is because by this point, she has admitted to Will that she is Kevin's natural mom, and that they've been having sex. (As we will see later in the analysis, Will had already found out about the incest prior to the relocation of Molly and Kevin.) This, in turn, is why Will suggests that Molly should now go with Kevin to her dad's in Montana - Will wouldn't be suggesting another relocation so soon, unless there was some very important reason, i.e., keeping Kevin safe from Molly.
