Widder Douglas becomes Huckleberry Finn's guardian after he saves her life from the criminal Injun Joe, feeling responsible for him out of gratitude and Christian duty. She lives in St. Petersburg, Missouri, with her sister Miss Watson and the enslaved Jim.

Her main purpose is to civilize Huck, whom she sees as an uncultured outcast. She enforces strict rules: prohibiting smoking and swearing, mandating regular meals with proper manners, and insisting on school and religious education, aiming to make him "regular and decent." Widder Douglas shows patience, contrasting with Miss Watson's stricter methods, and intervenes to prevent her sister from being overly harsh. When Huck fails expectations, like soiling clothes, she refrains from shaming him and expresses satisfaction with his progress.

Despite her kindness, her guardianship represents the societal constraints Huck finds stifling. She teaches him biblical stories, such as Moses liberating the Israelites, emphasizing spiritual values like helping others and selflessness. Yet, her moral framework contains contradictions: while advocating Christian principles, she simultaneously participates in slave ownership with her sister, illustrating antebellum Southern societal hypocrisy. Her failure to question slavery, despite teaching stories of freedom, underscores this ambiguity.

Her influence on Huck is complex; he acknowledges her fundamental decency but ultimately rejects the confinement of her structured life, leading him to flee. Her character does not undergo significant development and appears only in the narrative's initial segments across adaptations. Her legacy persists indirectly through Miss Watson’s later decision to free Jim in her will, reflecting potential moral growth within the sisters’ household, though Widder Douglas’s personal stance on this action remains unrecorded.