With whom does Carton sympathize while waiting to be taken to the tumbrel? Why is this person being executed? How is Sydney able to strengthen this prisoner? (From Book 3 Chapters 11-15)

Carton rides in one of the tumbrils, ignoring everyone but the girl whose hand he holds. The Vengeance looks for Madame Defarge at the guillotine in vain. Carton meets a seamstress accused of being a spy. Carton gives her strength and assureds her she will soon be at peace. He holds the girl's hand to the end and she thanks him for his support.