I think that it fits Sylvia's character for her to keep the change. Sylvia is the type of girl who is driven for her self, and motivated by her own self interest. Even after the revelation of the lesson, her statement at the end that she will not be taken advantage of by anyone is a reflection of her character at its essence. Sylvia's nature of wishing to advance situations for her own benefit is in demonstrated throughout the story. She speaks at length of wishing to take from others and advance her own agenda. It is in this where she wishes to keep the change and not give it back to Miss Moore. Sylvia is a product of a world in which one must do what one must do in order to survive. The transformative element that Miss Moore wishes to impart to the students is met with a sense of challenge out of Sylvia, who lives in an existence where her own benefit must be met. If anything, Sylvia represents the elements that have constructed reality in the manner that it is, the precise lesson that Miss Moore wants the children to understand. Empathy or a sense of widened scope of compassion is not something that Sylvia employs in her life, reason enough to keep the change. The ending is left open in terms of if this change is evident, as Sylvia wants to reflect about the lesson and think about what it has meant to her. In this, there might be something stoked in her that can enable her to change, but for the short term, her keeping the change is a reflection of her character.