In A Tale of Two Cities, Miss Pross is the staunch defender of Lucie Manette (later Lucie Darnay), her "ladybird," from the first time we meet her to the last chapter of the novel. In the beginning, Miss Pross feels the need to defend her young charge from the "businessman" Jarvis Lorry. Later, once the family makes its way to Paris, Miss Pross has more serious threats with which to contend.
Once Lucie and Jarvis are on the road (with Charles and young Lucie) heading out of Paris (and ultimately back to England), Madame Defarge showed up at the apartment ready to take Lucie into custody for an eventual trial and beheading. Jerry Cruncher has gone to get their hired carriage (for the two of them, plus all the luggage), leaving Miss Pross alone with the angry Frenchwoman. She understands, despite the language barrier, that Madame Defarge is willing to kill her to get to her ladybird. The two women have a literal hand-to-hand fight, and the gun which Madame Defarge produced goes off between them. The result is a dead Frenchwoman and a deaf Miss Pross. She never regained her hearing from that altercation, but she was glad to sacrifice for the family she loved.