The "Lovely Night" scene, as it's the only one where Cinderella, The Stepsisters, and even the Stepmother seem to all actually get along. Cinderella regales the sisters with how magical the ball felt (under the pretense that that's how she "imagines" it would feel) and the two don't hesitate to get swept up in the idea, both taking turns dancing with her and then with each other. Then their mother joins in herself and for a moment gives all three of them a genuinely affectionate smile before realizing what Cinderella's actually implying and shutting the whole thing down.. It really makes one wonder if they could've been a decent family together had the Stepmother just gotten over her man-issues.
The interactions between Ella and Gabrielle in the second act after Gabrielle realizes Ella attended the ball. They even address each other as sisters.