In the 1995 movie, 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."
Also in the 1995, how Sara get back at Lavinia- a proper mind screw by having her believe that she is cursed.
Sara's father remembering who he is, who Sara is, running out into the rain as the music swells, and just bellowing, " SARA! "
The 1995 film also has a scene where 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.
And Ermengarde's announcement from the book: "There WERE diamond mines. THERE WERE!"
From the novel: 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.