The author only describes Nya's appearance in the opening chapter of the book. She says that Nya is an eleven-year-old South Sudanese girl who is tall for her age. The reader can also presume that she is quite strong for her age as well, because she carries a bucket of water on her head from a pond to her town every day. At the end of the book, we find out that she is a member of the Dinka tribe, who look physically similar to the people of the Nuer tribe.
The Dinka and the Nuer did not look very different physically. You had to look at the scar patterns on people's faces to tell the tribes apart—Dinka scar patterns were different from those of the Nuer.
Perhaps the author decides against describing Nya's appearance in detail because the story is more about her external experiences than her internal ones. When she is not carrying bucketloads of water back from the pond, she is either caring for her sick sister, Akeer, or showing her sister how to do the various chores they need to do just to survive. She cannot afford to think about her own suffering, because it could quite easily mean the death of someone she loves. For example, her younger sister, just like many people in Nya's village, falls dangerously ill from drinking dirty water. When Nya's mother finally has the opportunity to take Akeer to the hospital, Nya reacts to her mother's pain:
Nya's mother nodded that she understood, but Nya could see the worry in her eyes. The water from the holes in the lakebed could be collected in tiny amounts. If her mother tried to boil such a small amount, the pot would be dry long before they could count to two hundred.
Life improves for Nya and her family at the end of the book. The town builds a well and starts to build a new school.