She was rather pretty and had been the best-dressed pupil in the procession when the Select Seminary walked out two by two, until Sara's velvet coats and sable muffs appeared... (4.6)
Oooh, Sara has all the best fashion when she comes to Miss Minchin's school. And of course her nice clothes win her an enemy at once: Lavinia.
"Well," she remarked, "I do not know whether your mamma would like you to tell stories to servant girls, but I know my mamma wouldn't like ME to do it." (5.16)
Lavinia cares way too much about whether people look "high class" enough for her to associate them. Really. Anyway, we guess we can't blame her, because she's obviously been learning this at home.
"Oh, Becky," she said. "I told you we were the same—only two little girls—just two little girls." (7.204)
On the outside, Sara and Becky look like they're the same, but Becky convinces her that it isn't so: Sara is still a little princess. Isn't this just a little contradictory? We're not actually sure if the book believes that we're all the same, or that some of us are actually special.
She did not look in the least like the rose-colored butterfly child who had flown about from one of her treasures to the other in the decorated schoolroom. She looked instead a strange, desolate, almost grotesque little figure. (7.157)
Sara's appearance truly takes a turn for the worse when her papa dies. You know its bad when your own narrator is describing you as "grotesque."
"To think that she was the girl with the diamond mines," Lavinia commented. "She does look an object. And she's queerer than ever." (8.17)
Lavinia is obviously the most compassionate and selfless person at the school. Obviously.
She had known that she looked odd and shabby, but until now she had not known that she might be taken for a beggar. (10.14)
Oh how embarrassing! The littlest member of the Large Family mistook Sara for a poor beggar due to her sad attire. Luckily, both of them handle it with real grace—like the well-bred children that they are.
"I didn't want you to know," Sara said. "It would have made me feel like a street beggar. I know I look like a street beggar." (15.104)
Sara is acutely aware of how un-rich she looks, but Ermengarde doesn't mind at all. Guess there are some benefits to being a little dim-witted.
It was the Princess Sara indeed. At least, since the days when she had been a princess, Sara had never looked as she did now. She did not seem the Sara they had seen come down the back stairs a few hours ago. She was dressed in the kind of frock Lavinia had been used to envying her the possession of. (16.81)
Take that Lavinia and Miss Minchin! Sara's back in fashion. (And, hey, where is our mysterious benefactor? We could totally use a new wardrobe.)
The Indian gentleman's carriage, with its tall horses, drew up before the door of the next house, and its owner and a little figure, warm with soft, rich furs, descended the steps to get into it. (19.24)
Wow. She really does like those sumptuous fabrics and furs, doesn't she? Why all the emphasis on the clothes? And do you notice how Burnett describes all these clothes with texture detail? It not actually about how they look, but how they must feel: "soft," "warm," and "rich." Mmm, makes us want to take a nap.
"…Excuse the liberty, miss,"—to Sara—"but you look rosier and—well, better than you did that—that—"
Sara looks so different from her street-rat self by the end that the bakery woman can hardly recognize her. But she's still the same person underneath.