Why is Darby Trixle upset because Cam got the job as the associate warden in the novel, Al Capone Does My Homework?

Darby Trixle got upset that Cam got the job as the associate warden because he wanted the job for himself. In turn, Darby is one of the residents of Building 64 who accuses Nat of being responsible for setting fire to the apartment in which she and her family lived. It turns out that Darby paid Donny to set fire to the apartment.