Nancy might be the most complicated character of the novel. Despite being a relatively minor character, she has a very important role to play – she’s the source of the information about the plot between Monks and Fagin to ensnare Oliver.
Why does she help Oliver? What’s the turning point for her? Well, that’s what’s so complicated. She seems to be reminded of her own lost innocence when she looks at Oliver. Soon after Oliver is stolen back from Mr. Brownlow’s house, she jumps to his defense for the first time, and yells at Fagin: "I thieved for you when I was a child not half as old as this (pointing to Oliver). I have been in the same trade, and in the same service, for twelve years since; don’t you know it? Speak out! don't you know it?" (16.82). This passage is the first that tells us Nancy’s age: if Oliver’s around ten or so at this point, and she’s been in Fagin’s employ since she was half that age, she must have started when she was five. And so now, twelve years later, she’s seventeen. Awfully young to be as jaded as she is, don’t you think? She tells Rose later that she’s younger than she looks, though "old in sin."
Dickens rarely gives us a glimpse of what Nancy’s thinking or feeling – he tells us what she’s doing, but that’s about it. We have to infer the rest. So when she says or does something that looks inconsistent, or hysterical, we have to be almost as befuddled as the rest of the gang. For example, when Sikes is trying to get her to stop taking Oliver’s side, he says:
"Do you know who you are, and what you are?"
"Oh, yes, I know all about it," replied the girl, laughing hysterically, and shaking her head from side to side with a poor assumption of indifference. (16.75-76)
So here, Nancy’s basically laughing because she can’t do anything else – she hardly finds it funny. But again, Dickens doesn’t actually say what she’s thinking or feeling, or give us what literary critics call a "sympathetic inside view." He describes only what her actions are as a perceptive observer might view them.
It’s also important to note that Dickens never – not once – uses the word "prostitute" or "whore" to describe either Bet or Nancy. This is the closest he comes, and it’s through Sikes, who asks Nancy if she knows "who" and "what" she is. The implication is pretty obvious – she’s a prostitute, and therefore hardly a moral person to take Oliver under her wing – but Dickens never comes out and says it. Why is that? Dickens doesn’t shy away from showing the grisly murder in all its gory detail, or from describing thefts and frauds and other crimes. Is it just Victorian sexual repression that keeps him from saying that Nancy is a prostitute? That could be part of it. After all, Dickens wants his audience to feel sympathy for Nancy by the end, and a Victorian reader might object to feeling sympathy for a whore.
When Nancy meets with Rose alone, and then with Rose and Mr. Brownlow at the bridge, she has to make a difficult choice. They offer her a safe passage to a foreign country, where she could live in peace and solitude, far from her old life, and secure from Fagin, Sikes, and the others. She’s terrified of Sikes, and loathes Fagin. So why does she say no? Is it pride? Does she not want to take handouts from them? Maybe. Earlier in the novel, before her first conversation with Rose, we’re told that pride is "the vice of the lowest and most debased creature no less than of the high and self-assured" (40.52). So OK – it could be pride.
Or is it love? She tells Rose that it is at the end of their first meeting. She explains:"When such as me, who have no certain roof but the coffin-lid, and no friend in sickness or death but the hospital nurse, set our rotten hearts on any man, and let him fill the place that parents, home, and friends filled once, or that has been a blank through all our wretched lives, who can hope to cure us?" (41.103)
Sounds like a pretty appalling version of love, but OK – that could be it. Or is it Fate with a capital F? Nancy seems to think so at their final meeting – she says, "I am chained to my old life. I loathe and hate it now, but I cannot leave it. I must have gone too far to turn back […]" (46.74). This idea of having "gone too far to turn back" seems pretty much in keeping with the rest of the novel – once you turn down the wrong path, there’s no turning back, even if it means returning to your violent and menacing lover only to be brutally murdered. This novel seems to take a pretty bleak view of forgiveness and redemption, despite the apparent hopefulness of the final lines.