I think it would be interesting to see some of the development of Melinda's character through the eyes of someone else. The most perceptive of these would seem to be Mr Freeman. Perhaps a scene where he may reflect on his observations of this unusual young lady would be fitting.
If the question seeks to bring out the construction of an additional scene from the work, then I think that there are many different directions one can go. The novel ends with the idea of social solidarity being evident. The presence of the Girls' lacrosse team when she confronts Andy, Mr. Freeman's opening of a discussion with her and she reciprocating it are all examples of how personal trauma has led to the idea of social solidarity and bonding. I think that an additional scene that would make sense is that Melinda starts some type of support group for girls who have been the targets of unwanted sexual advances. I think that this contunes the flow of the story because the primary trajectory of the narrative has been the idea of moving from privatized pain to public acknowledgement and reclamation of voice. This trend continues if Melinda is a logical extension of this and begins a support group. It also is quite relevant. At a high school, a male student constructed a list posted on Facebook about girls at his school and divulged sexual acts performed, rankings on physical appearance, and circulated the list to many. The girls, when confronted with their presence on the list, were shocked and dismayed. In response, some of them formed their own support group where they took the opportunity to "speak" about their feelings. Something similar could be initiated by Melinda to ensure that no one else feels that they cannot "speak."