Friendship might also be a theme. Maybe Laura has a secret friendship that she's been hiding, and the story could revolve around the reasons for that secrecy, how it affects her, and how she manages it within her other relationships.
Another theme could be mystery. Given that it's a 'secret' story, there's likely an element of the unknown. It could involve Laura trying to solve a mystery, like a missing object or a strange event that happened in her town.