"What--sort of thing?" Miss Amelia ventured.
"It might almost be called defiance," answered Miss Minchin, feeling annoyed because she knew the thing she resented was nothing like defiance, and she did not know what other unpleasant term to use. "The spirit and will of any other child would have been entirely humbled and broken by--by the changes she has had to submit to. But, upon my word, she seems as little subdued as if--as if she were a princess."
"Do you remember," put in the unwise Miss Amelia, "what she said to you that day in the schoolroom about what you would do if you found out that she was--"
"No, I don't," said Miss Minchin. "Don't talk nonsense." But she remembered very clearly indeed.
- A Little Princess, chapter 16
This episode is part of a series of episodes that deviates from the novel for a bit. What is most important about this episode is this scene here, where Ermengarde confronts Lavinia about why she treats Sara the way she does. The answer, while not surprising, is also rather symbolic of the series as a whole and finally rounds out Lavinia's character. It also shows how Ermengarde has changed since the beginning of the series; doing what she did would have been unimaginable in the beginning.
You can obtain this episode from your standard anime torrent indexing sites.