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.
Quote 4
"My husband, fellow-citizen, is a good Republican and a bold man; he has deserved well of the Republic, and possesses its confidence. But my husband has his weaknesses, and he is so weak as to relent towards this Doctor." (3.14.4)
Madame Defarge’s loyalties are more complicated than the sort of family-centered loyalties we see in the Manettes. Sure, she likes her husband and the revolution. She cares more, however, about her own revenge.
Quote 5
There was a character about Madame Defarge, from which one might have predicated that she did not often make mistakes against herself in any of the reckonings over which she presided. (1.5.20)
Madame Defarge becomes her own form of judge and jury over the course of the novel. Her version of justice, which demands unremitting revenge, could be seen as the downfall of the new Republic as a whole.