Kathryn Stockett's work is fiction, according to Republic World. The author has repeatedly stated that her novel is fictional, but the similarities between Ablene Cooper (her brother's maid) and Aibileen Clark (the main character in the novel and film) are too hard to ignore.
According to Screen Rant, not only do Cooper and Clark share the same name, albeit with a different spelling, but their stories are also similar as well. In the film, Clark returns back to work five months after her son is killed in an accident. Cooper's son, Willie, passed away from leukemia in July 1998 three months before she worked for the Stockett's, according to the New York Times. A little coincidental, right?
The descriptions of the book's character and the real-life housekeeper are similar as well. According to the New York Times, both maids—real-life and fictional—both have a gold tooth and are called "Aibee" by the white children they care for.
While repeatedly Stockett claims The Help is fictional, the similarities between Cooper and Clark are clear. So, yes, while Stockett says The Help is fictional, the real answer, may be a bit more complicated.