What is the theme in Calico Bush by Rachel Field?

Strength of character is a theme. Marguerite is still a young child when her grandmother and uncle, her only family after the death of her parents, decide to migrate to Canada. Marguerite's uncle is full of dreams for their future, but these dreams die when he and the grandmother both die within months of one another. Marguerite finds herself all alone at the age of twelve with no family or money to care for her. Marguerite is sold to a family who promise to provide for her in exchange for her help with their home and children.