It's true--the development of the executive centres was not mentioned and should have been. However, I thought priest-counselor said something insightful. He pointed out that Hannah’s posthumous narration of all her grievances might suggest to the adolescent mind that suicide is the prelude to a satisfying retribution story. 

He noted: "The permanence of death must be emphasized for children who developmentally do not understand death. Even teens with a better understanding may not have the maturity to accept the reality of death’s effects."

Anyone who has ever lost someone to suicide knows this is not how it works, that shattered survivors spend years coming to terms with why, and that the only response from the universe is silence.