I had to edit down the original question. I invite you to resubmit the other part in a separate question as both really strike at the heart of Anderson's work. In the end, why Melinda is silent is central to understanding both the implications of the work and her characterization with in it. I tend to think that Melinda is silent because the world has no interest in what she has to say. Consider that Melinda is silenced by nearly every possible force in the exposition of the book. Socially, the kids target her because Melinda called the cops to bust up the party. Intellectually, she is silenced by her teachers who seem more concerned with seeking to conform Melinda to their standards as opposed to understanding who she really is. Parentally, Melinda finds that she has little sanctuary with them as her grades plummet. Consider that she has no place to sit in the lunchroom, confirming that she is silent because no group validates her voice. At the same time, during the pep rally, when the kids are cheering, Melinda screams into her hands. She is silenced. No one hears her. This is an embodiment of how Melinda is silenced by the world because she is seen as not having a part in it.