By wondering and daring to ask about May's sensitivity, Lily is making an important decision.  She thinks to herself, "The last thing I wanted was to be like (May), but I didn't want to be like T. Ray either, immune to everything but his own selfish life".  Lily realizes that if she continues to shut out her real feelings and pain, she will become like her father, cruel and cold.  The alternative is to open herself up to sensitivity and suffering, and by seeking to understand May she begins to explore that option, and the possiblity that sharing her sorrows might make them easier to bear.  Lily appears to have made her decision to trust the Boatwrights and let them know the truth about herself when August warns her about May's trauma, "'It's not a pretty story'", and Lily responds with a smile, "'My story's not pretty either'" (Chapter 5).