Nancy is the strongest representation of the social conditions of the time period.
Although Oliver is the strongest sympathetic character in the book, his situation changes dramatically once his family heritage is revealed. As soon as he is found to be of noble birth after all, he is rescued. This is not the same for poor Nancy. She is the perfect example of a victim of the social conditions of the day.
Dickens had great sympathy for prostitutes and women in poverty. He even created a shelter for these “fallen women.” This is one of the reasons that Nancy is one of the most sympathetic characters in the book. The first description of Nancy and Bet is fairly innocent.
They were not exactly pretty, perhaps; but they had a great deal of colour in their faces, and looked quite stout and hearty. Being remarkably free and agreeable in their manners, Oliver thought them very nice girls indeed. As there is no doubt they were. (ch 9)
Colored by Oliver’s naïve impressions, we see Nancy and Bet from an innocent perspective. They are friendly but dress a little sloppily. Yet they are just as much under the thumb of Fagin as Dodger and the boys. They also suffer the abuse of their men.
Nancy’s relationship with Sikes is intended to generate pity. She is abused constantly, and although she loves Sikes there seems to be little affection in him. She doesn’t want to help Sikes kidnap Oliver, but basically has no choice.
And Mr. Sikes was right. By dint of alternate threats, promises, and bribes, the lady in question was ultimately prevailed upon to undertake the commission. (ch 13)
Ultimately, Nancy’s attempt to protect Oliver from the life she knows is in store for her leads to her doom. She tells Brownlow his story, and when Sikes finds out he kills her. Nancy does not escape.
Nancy never had any options. Her society has thrown her away, and she has little chance of recovering her dignity or returning to a life of safety and honor. Most Victorians would not have had sympathy for prostitutes, and Dickens’s skillful use of Nancy is designed to change their minds and help them understand the social conditions of the time, and the lack of options for people like her.