Answer :
There is some parallel between Sissy’s story and Dickens’ own. When he was 12 years old, Dickens was sent to work at Warren’s Blacking Factory (Coketown, come on) after his father was imprisoned for debt. Claire Tomalin asserts in her superb recent biography about Dickens that, when he was rescued by his parents neither he nor they uttered a single word about it to one another. So I suspect that Dickens was strongly attached to Sissy in a very personal way. And for me, a world without Sissy Jupe would be a world without Dickens.
Sissy represent the good force in the novel, she is kind, caring and loving, she has difficult events to bear in her life, however, even after her father abandoned her and she had to learn the Gradgrind philosophy she continues being a positive person, and at the end, she is the only one who gets a happy marriage and children.