As most Heroes followers could have guessed, her fear of the "Boogeyman" will play a prominent role in season two.
Here's what Creator Tim Kring had to say about the part of Molly, also known as the Heroes "tracking device" for her unique super power...
To be honest, we actually thought her re-entry into the show was going to be a lot sooner, and it got pushed back. While we knew she was coming back, in all seriousness and candidness we didn't know it was going to be that late in the series. I would pay some attention to Molly Walker and what she represents as an important clue as to where [Season 2] is going.
That'll be revealed pretty much in the season opener, but this idea that Molly Walker and Suresh's [Sendhil Ramamurthy] sister had similar ailments is a key part of where this story is going in the second season.