Trish comes home, finds her family dead, and doesn't call the police. Instead she runs to her boyfriend, to find her cheating, and other big stuff happens. (I'm glossing over to get to the important, unrealistic to me part.)
She's talking to her friend who finds her, and asking what she'll do. She just blurts out that she goes home to find her parents dead, and that she thinks they killed themselves. Neither of this sixteen or so year old girls thinks to call the police about, say, where Trish will stay? What the what?
Neither of them are concerned that this could be something the police need to investigate, and that the longer they don't call the police, the more chance that shit could get fucked up real bad?