As several feminist critics have already written about Ann Petry's work, your first step should be consulting the MLA International Bibliography to familiarize yourself with existing scholarship.
One debate quite active in the 1990s and into the beginning of the 2000's concerning applying feminist scholarship to Petry was the question of whether feminist literary theory, as initially developed by white middle class Europeans, was applicable to black writers. In response, a movement called "Africana criticism" was developed to study the intersections of African-American and female cultural heritage.
One issue to consider in Petry is how she negotiates the dual marginalization of black and female, and how her unusual biography (from a New England rather than southern rural upbringing, middle class education, etc.) affected the way she percieved Harlem and made her viewpoint distinctive.