Why does Polly attempt suicide in the novel, All We Ever Wanted?

Finch accuses Polly of being crazy and emotionally disturbed. He tells Lyla that she had a good deal of emotional problems including cutting herself. After Finch accuses Polly of taking the picture of Lyla because she was jealous and spray painting the word “slut” on Lyla’s front porch Polly tries to commit suicide. Before her suicide attempt, Polly told Lyla that Finch had pictures of other girls on his phone as well as pictures and videos of him having sex with Polly. Polly sent Lyla a picture of Lyla with Finch’s penis laying across her face. Because Lyla and Nina warned Polly’s parents, Polly survived her suicide attempt.