Although she complains and can be immature, stamping her foot petulantly when her mother wants to send her away at the plague"s beginning, "Old Mattie" has strong character traits which only need time and experience to develop into fruition. Intelligent and ambitious - "clever" as she puts it, she takes care of the coffeehouse accounts and has detailed plans in her mind for its potential expansion. She is a capable worker, handling the shopping and the many tasks necessary to keep the guests happy with efficiency and aplomb. Despite differences with her mother, "Old Mattie" has a good heart, loves her grandfather, and appreciates Eliza, who tries to make her way easier with little treats like sugar in her oatmeal.
Mattie grows up fast during the "fever", responding with resilience and common sense when she is left with her grandfather to care for - her love for him leads her to defend his life with a sword - and then on her own. When the the plague finally ends and her mother comes home an invalid, "New Mattie" accepts responsibility for caring for her and little Nell as well as running the coffeehouse. Her industriousness and "cleverness" enable her to handle the myriad tasks that fall to her, even while her loving spirit leads her to do a little extra so Eliza can get much-needed respite. Mattie is capable, and looks to the future with confidence and hope.