I definitely agree that the chosen passage is a great passage that viscerally shows the turmoil that is happening within Melinda. The quote does a great job of showing the pain that she is in, the desire to withdraw from everything, and the desire to speak out and tell someone about her emotional pain and what caused it.
To answer your final question about whether or not there is more to it, I would say yes, there is more to it; however, I don't think that you need to worry yourself about searching the text for something beyond the initial set up that you have already given yourself. The Enotes prompt says that you want to write a paper, and you desire it to be based around the provided quote. I think you have a great starting position and handle on Melinda based on that single quote.
Your next task is to compose a thesis that gives your paper direction and will allow the incorporation of that quote as supporting evidence at some point. I would recommend something like the following thesis statement: "Although Melinda desires to hide away herself and her feelings, she also deeply desires to speak out and share her emotional turmoil with somebody." The quote supports this thesis, and the text is filled with other instances of supporting examples that show Melinda's inner conflict about how to tell the world about the danger that is Andy.