WMG / Nothing More To Tell

Brynn is wrong about who the killer is at the end

Nothing about Charlotte's attitude while listening to and denying Brynn’s theory is particularly different from the way the character acts for the rest of the book (which also isn't terribly discreet for someone who could get arrested for murder) except for getting nervous when Brynn deduces that she thought Mr. Larkin was threatening Shane. A large part of Brynn's conclusion is based on Motive = Conclusive Evidence. While the final chapter does confirm that Charlotte knew a lot more about what was going on than anyone realized and sent an anonymous note meant to get Mr. Larkin fired, there's a big difference between doing that and killing someone in a fight, even by accident. Overhearing Mr. Larkin and Uncle Nick's argument about the note could just as easily have made Charlotte frightened and quick to get away from the area instead of angry and determined to stick around to pick a fight. It's never explicitly confirmed that she didn't meet up with Shane until after the murder, and even if she didn't, she might have really thought that Shane was the killer and been trying to protect him. Alternatively, she could have thought that Nick was the killer and blamed herself for provoking the fight between him and Mr. Larkin. Finally, the last couple of chapters explicitly mention that Brynn and Tripp want to find an alternate explanation to Tripp’s mother being guilty, regardless of her many flaws. This desire for them to find a culprit who Trip wouldn't have to feel guilty over makes them a bit biased in their scrutiny toward alternate suspects (especially Brynn, who dislikes Charlotte for the most part and has little trouble believing the worst of her). While none of this is proof that Charlotte really is innocent, it is enough to make the ending more ambiguous.