I edited down the original question. I think that one of Anderson's primary motivations in constructing the character of Melinda in the way that she has is to show how the act of rape creates an individual voice that is different than what is shown to others. Melinda being raped causes her to portray an image on the outside different than one that is on the inside. It is evident that Melinda has a voice and has something to say. Yet, the act of being raped is one that has twisted herself in so many different ways that the perception of who she is on the outside is not who she is on the inside. Melinda struggles to right her own sense of self after the rape. It is for this reason Melinda portrays herself differently, primarily because she believes that no one would understand or would want to understand what happened to her and what she endured. The challenge for Melinda is to demonstrate that there is a voice within her that can be heard. While on the outside she might appear that she does not want to speak, it is the internal drive within her to be heard and to be understood as one whose voice needs to be validated. Andy, "IT," has done a good enough job in silencing and discrediting her. For this reason, the final confrontation in the closet is critical. He believes that he can silence her again. He believes that he can continue the fact that her outward appearance is reflective of a voice that can be discarded. When she demands to be heard and externalizes this to others, it is a moment in which she has been able to ensure that what is on the inside is externalized on the outside. For this reason, the fundamental struggle in the novel is for Melinda to be able to reconcile what is within with what is shown on the outside, a desire to bring convergence to an existence in which the physical and social rape of an individual has brought divergence.
Its been years since I read this book or did a lesson on it, but if I remember correctly, Melinda was raped at a party by a guy that Heather likes. When Heather and Rachel find out, they sort of stop being her friend. Melinda doesn't talk at all to anyone after that event. The comparison of there three personalities are typical of that age group and status. They are all attention seeking teenagers trying to fit in and be cool with boys. When Melinda replays the night in her mind, she knows that she wanted to make out with the guy, goes into a room with him at a party, but doesn't want to go all the way. The mood and her choices kind of lead you to believe that she is not telling the truth. However, you have no reason not to believe her either. After she stops talking, you see a different side of her that she never let out when she was trying to fit in. You see an artistic side of her when she finds a place in the school where she can be alone. In the other two girls, you see them still trying to fit in with the boys. One of them gets involved with the guy who raped Melinda. She ends up having sex with him. The other girl Rachel is the highest ranking girl of the three. Her status is popular among all her friends and she sort of sets the stage for what the majority will believe. If she says it, then it must be true. However, she also has a very close knit family and not much freedom so most of what she shows others is a rebellion against what is trying to be forced upon her at home.