First, I would not necessarily identify characters in Harriet Wilson's book as representing "North" or "South." It was, in fact, in the northern states that the great majority of sentiment in favor of abolition existed, and it was the South that practiced slavery and seceded from the Union in order to uphold it. But not all northerners were progressive, and not all southerners were as cruel to African Americans as the majority were. In Wilson's story, Mrs. Bellmont is probably the cruelest and most regressive of the characters. She is sadistic toward Frado both verbally and physically. It's part of Mrs. Bellmont's overall nature, but it's clear that such people would take out their aggression and abusive tendencies chiefly upon black people. This was the dynamic of life in the southern states, unfortunately, and remained so even after the Civil War brought the "peculiar institution" to an end, though without granting proper rights to the freed people.
Both Mr. Bellmont and the Bellmont son Jack are more moderate In their behavior to Frado, but the only character we would focus on as a symbol of progressiveness is Samuel, an escaped enslaved man Frado meets in the North, who is involved in the abolitionist movement. In general, however, the story illustrates that Frado is basically alone and has to rely on herself for survival. The novel paints a realistic and grim picture of antebellum life.