Had Hetty made "a show of herself" by performing, Phyllis would perhaps have made a grievance of it to her parents.

Stung for a moment with the consciousness that this was true, before she had had time to persuade herself of the contrary, Phyllis grew white with anger.

The injury she could least forgive was a hurt to her self-complacency.
"She must apologize, Miss Davis, or I will go to papa," said Phyllis, disdaining to glance at Hetty, but looking at her governess.
Miss Davis was troubled.
"This is all very painful," she said.

"Hetty, you had better go to your room till you have recovered your composure.

Whatever may have been your motives last night you have now put yourself in the wrong by speaking so rudely." Hetty flashed out of the room, and Phyllis, quiet and triumphant, turned to her lesson-books with a most virtuous expression upon her placid face.
Hetty wept for an hour in her own room.