A brief episode in Brad Gooch's biography of her is illuminating:
"I see I should ride the bus more often," she wrote to Betty Hester, in 1957. "I used to when I went to school in Iowa, as I rode the train from Atl. and the bus from M'ville, but no more. Once I heard the driver say to the rear occupants, 'All right, all you stove pipe blonds, git on back there'. At which moment I became an integrationist."
Not conclusive, of course. We'll never really know what she thought. But this, at least, offers better evidence of her opinion than the facile transposing of the views of her characters to her.