Who is Nell in Fever 1793 by Laurie Halse Anderson?

In Laurie Halse Anderson's Fever 1793, Nell is a young girl who becomes orphaned and homeless after her mother dies of yellow fever. Matilda, the novel's main character, discovers her crying in the street as she wanders her city in the hopes of finding someone who can help her. She decides to help Nell, and carries her through the streets until Matilda finds someone she knows: Eliza, her family's former cook. Eliza allows the two to stay with her briefly, but when she suggests that they find an orphanage, Matilda refuses and moves back into her abandoned family home with Nell. When Nell becomes sick with yellow fever shortly after that, Matilda nurses her back to health using the methods she remembers from the hospital she stayed in.