Quote 1
"I care nothing for this Doctor, I. He may wear his head or lose it, for any interest I have in him; it is all one to me. But, the Evrémonde people are to be exterminated, and the wife and child must follow the husband and father." (3.14.6)
Madame Defarge sees her sister’s rape as a family crime, one that must be repaid by an entire family. Her sense of justice pays no attention to the actual perpetrators of the crime.
Quote 2
"But it is your weakness that you sometimes need to see your victim and your opportunity, to sustain you. Sustain yourself without that. When the time comes, let loose a tiger and a devil; but wait for the time with the tiger and the devil chained—not shown—yet always ready." (2.16.39)
Madame Defarge shows restraint where her husband shows passion. At the moment, this seems like a good strategy; it also foreshadows her pitiless treatment of the Manettes later in the novel.
Quote 3
"Then tell Wind and Fire where to stop," returned madame; "but don't tell me." (3.12.36)
By the end of the novel, Madame Defarge is more of a supernatural force than a natural one. She’s ultimately terrifying in her unwillingness to deviate from her plans for revenge.