What is the main conflict in The Birchbark House by Louise Erdrich?

A brief prologue describes how a group of canoeing fur traders abandons the sole survivor of a smallpox outbreak, a baby girl, because they're afraid of being infected with the disease that killed everybody else in her Ojibwa community. As he goes, however, one of the traders imagines that if anyone would come back to rescue the girl, it would be his strong-willed, fearless wife Tallow.