When school bully Lavinia accuses Sara of making up "fairy stories" about Heaven, Sara primly tells her that no one knows what Heaven is really like, but unless Lavinia starts being kinder to people, she'll never find out - a fairly classy schoolgirl way of telling Lavinia to go to hell.
When Lottie asks Sara to tell her stories about the diamond mines, Lavinia snaps and says that she would like to slap Lottie. Sara rounds on her, proving that she dislikes Lavinia, too, but is still the better person.
"Well, I should like to slap you - but I don't want to slap you. At least, I both want to slap you - and I should like to slap you - but I won't slap you."
After Sara is left poor on Miss Minchin's hand, she keeps her on as a scullery maid and girl-for-all to get some use out of her. Sara is about to leave, when Miss Minchin stops her.
Miss Minchin: Stop! Don't you intend to thank me? Sara: What for? Miss Minchin: For my kindness to you. For my kindness in giving you a home. Sara: You are not kind. You are not kind, and it is not a home.
Sara has told the younger children the story of King Alfred getting hit by a neatherd's wife for burning some cakes and her shock at learning that she just assaulted her monarch. While she's smiling and thinking, Miss Minchin boxes her ears, just like it happened to Alfred. After Sara explains that she wondered what Miss Minchin would do, if she learned that Sara was actually a real princess and could do whatever she wanted, she'd never dare to raise her hand against her. Miss Minchin demands that Sara apologize.
"I will beg your pardon for laughing, if it was rude, but I won't beg your pardon for thinking."
Miss Minchin learns that Sara's wealth has been restored, and has increased manyfold, and she tries to appeal to Sara to come back to the school. She says she'll be a parlor-boarder again and to do a duty to her dear father, who left her in Miss Minchin's care, after all. Sara takes a step forward, like she will return, but then remembers how she was treated when she was penniless.
"You know why I will not go home with you, Miss Minchin. You know quite well."
Ermengarde's announcement: "There WERE diamond mines. THERE WERE!"
The scene in which Sara witnesses Miss Minchin abusing a little boy who works as her chimney sweep. In order to get back at Minchin, Sara and Becky climb up to the school roof and dump copious amounts of soot through the parlor fireplace flue while Minchin practices the harp. The result is a veritable mushroom cloud of soot and a wailing Minchin.
Midway through the film, Sara's friends engineer a plan to get back the locket Miss Minchin took from her. This involves a Cacophony Cover Up (Lottie's tantrum), sneaking into the headmistress' office, and going through her desk and shelves to find the locket. What makes the whole scene more awesome is that the girls are mere seconds from being caught, until Becky, who is outside the office, screams and tells Minchin she saw a mouse.
Sara's speech to Minchin: "I am a princess. All girls are. Even if they live in tiny old attics. Even if they dress in rags, even if they aren't pretty, or smart, or young. They're still princesses. All of us."
Sara's method of getting her revenge on Lavinia - a proper Mind Screw by having her believe that she is cursed.