Jennifer Nansubuga Makumbi sets her blazing new novel, “A Girl Is a Body of Water,” in the conflicted nation of her adolescence: 1970s Uganda, under the brutal rule of dictator Idi Amin. Protagonist and heroine Kirabo is 12, growing up safely and happily in the village of Nattetta, raised by her paternal grandparents. She doesn’t know who her mother is, and her father, Tom, flits in and out, busy with his position on the country’s Coffee Marketing Board…