Scarlet Sister Mary won the Pulitzer as a weird switch. The Pulitzer committee wanted to change the scope of the Pulitzer from "a novel which presented the wholesome atmosphere of American life and the highest standards of American manners and manhood" to become "a novel which preferably shall best present the whole atmosphere of American life".
And, yet, even in this, Scarlet Sister Mary fails. Peterkin's depiction of uneducated blacks living in the low country of South Carolina in the early part of the 20th century is hardly believable, given today's understanding. They are the progeny of slaves who stayed where they had lived because they had no choice to go anywhere else. What could they possibly do? They continued living largely as their ancestors had.
Whites are not a factor in the book except as occasional mention that they do exist. This is not a criticism, just an observation. Peterkin's description of the life of these people, particularly that of Sister Mary, really is fiction. She suggests picking cotton is easy, more like a party, and everyone enjoys doing it. The life of Mary, a mother of 10 children with no father in the home, seems almost easy. More like a teenager bouncing through life. Some deep heartache, but even that passes.
There is a reason that Scarlet Sister Mary does not appear on any "best works" lists. An easy read, though.