In I know why the caged bird sings what does Mrs. cullinan do that deeply offends marguerite? How does marguerite show her displeasure

Marguerite is working as maid at Mrs. Cullinan's house. She does't even try to remember Marguerite's name and insists in call her Mary. Also, Mrs. Cullinan behaves rudely with Marguerite, this strongly upsets Marguerite who is unable to quit the job because her mother doesn't let her, so she decides to drop Mrs. Cullinan's favorite dishes to get fired. After that Mrs. Cullinan starts to call her Margaret, which Marguerite accepts because is closer to her real name and she was happy that the woman admitted that her name wasn't Mary.