Thanks for your question!

Chapter 23 of Fever 1793 by Laurie Halse Anderson finds the protagonist, Mattie, staying with Eliza, Eliza's husband Joseph, and their two boys, and helping to care for those who have been sick (including the boys, Joseph, and the young girl, Nell, whom Mattie found orphaned).

To answer your question with one example, consider that Mattie, who began the book all but a child herself and nearly too immature to be counted on to accomplish whatever tasks her (admittedly demanding) mother set before her, has by now voluntarily taken on the care of others around her, who are not even her own family. Therefore, she is learning to be far less selfish than she once was, especially since caring for the deathly sick is such a grueling and often thankless task, fit for none but those who are willing to abase themselves and set aside their own preferences.

Mattie's own mother calls her "lazy" in the very first chapter; Mattie ignores, for a time, her mother's command to get up for the day, deciding that her own desire for "[a] few more minutes' rest" is more important than anything her mother could want of her; and Mattie makes thoughtless, disrespectful assumptions about Polly, their serving girl, and her lateness for work, anticipating that Polly is dawdling and "eyeing . . . the blacksmith's son" instead of being punctual (when Mattie herself has absolutely no moral ground to stand on, since she's also dawdling just getting out of bed). By chapter 23, though, Mattie's outlook (and work ethic) has become much more mature.

You might also, in considering how to thoroughly answer your question, think about the decision Mattie makes on behalf of Nell in chapter 23, the orphaned girl she's taken under her wing, when Mother Smith comments that it would be selfish for Mattie to keep Nell and love on her and then abandon her to an orphanage after Nell has come to trust her in return. What does it say about Mattie's growth out of her own self-serving childhood that she turns out to be willing to give Nell up, believing that an orphanage might really be in Nell's best interest, even though Mattie will miss her terribly?