in a tale of two cities, what expalnation does dr. manette's letter provide for the actions and vengefulness of madame defarge?

Okay, this is a little fuzzy in my head but I think it goes something like this. Madame Defarge's father brother, brother in-law and sister died at the hands of the Evremonde brothers. They were nasty aristocracy who basically picked on this family in the worst way. The doctor knows this because he was kidnapped by the same brothers to save the two left alive (beaten in the worst way). This is why Madame Defarge is so pissed off. She wants vengeance against this family and all who follow their line.