This post originally appeared on my LiveJournal in this entry, which may include a lively discussion in the comments.
Chapter 4 is entitled "Lottie", telling us which of Sara's satellites we'll be introduced to this time. But the initial part of the chapter concerns itself with setting up Sara's common sense, self-awareness, and charity in several senses.
This is initially explained by the omniscient narrator, who points out that the favoritism and flattery that Sara received at the school would be more than enough to turn an ordinary girl into a spoiled brat. Miss Minchin is once again emphasized as two-faced: secretly disliking Sara but publicly going rather over the top to indulge and pamper her, in the belief that this would cement Sara's enjoyment of her school experience.
Sara, we are shown (in a conversation with Ermengarde), is instead quite aware of both her privilege and her luck. "A lot of nice accidents have happened to me. … Perhaps I have not really a good temper at all…and no one will ever know, just because I never have any trials." But she is secure enough in her position that she's friendly to everyone, generous to beggars that she meets on the street, and even willing to suggest that Mean Girl Lavinia acts horrid only due to growing pains. And as the most salient sign of her generosity and charity, Sara is willing to attempt to befriend "the baby of the school", Lottie Lay. But that we will cover in the next entry.
At the moment, I want to indulge in a critique of literary style. (Because this is a critical re-read, after all.) The thing that peeves me the most about Burnett's prose in this book is her tendency to use formulaic strings of adjectives. In particular, the word "little" is vastly over-used and could probably be eliminated 90% of the time. The strings of adjectives themselves stand out as being just over the edge of what is needed: A clever little brain, a friendly little soul, a motherly young person -- all those from the present chapter. But earlier strings that irritate me every time I encounter them include: "a queer old-fashioned thoughfulness" (in fact, one could do an entire analysis of the use of the words "queer" and "old-fashioned" in this work), "her handsome, rich, petting father", "a rash, innocent young man", "a queer, polite little voice", "a funny, old-fashioned child" (I mean, what the heck does that even mean?), "a very nice, intelligent, middle-aged Frenchman". Looking at them like that, I'm not even sure why the constructions irritate me so much.
In any event, the exploration of Sara's character is then framed by contrasting her with Lavinia, via a conversation between Lavinia and her BFF Jessie. Lavinia, it is explained to us, had been the de facto leader of the students prior to Sara's arrival, evidently due to equal parts seniority, a spiteful domineering personality, and heretofore being the best-dressed "show pupil" given special privileges. Sara undermines her position without meaning to by virtue of being richer and smarter than Lavinia, but more consciously by Being Nice. Not nicey-nice, for she isn't above speaking sharply to Lavinia in defense of other students, but genuinely kind and generous.
This is the primary theme of these early parts of the book: in those areas where Sara has agency, she uses that agency to make the world a better, happier place for those around her, as best she can. And the lengths she's willing to go to do so are detailed in her encounter with Lottie, to be covered in the next segment.