How would you describe the main character in Nightjohn?

Sarny is the main character in Nightjohn. In the story, Sarny is a spunky, perceptive, and resourceful young girl.
Sarny's courage and resourcefulness is clear from the beginning of the story. She spends time listening to the conversations of Margaret and Alaine as she works in the flower beds. Margaret is Clel Waller's wife, and Alaine is Margaret's sister.
When both women express their disgust at Clel purchasing yet another slave, Sarny's ears perk up. Her unobtrusive spying nets her some interesting information. She learns that slaves are expensive and that a slave can cost over a thousand dollars.
By listening, Sarny learns about the world around her. Her determination to thrive is evident, and her efforts are soon rewarded.
The text tells us that Sarny eventually makes Nightjohn's acquaintance, and it is from him that Sarny learns how to read. For her part, Sarny understands the dangers of being literate. However, she persists, and by the end of the story, Sarny helps Nightjohn teach slaves from surrounding plantations how to read.
In all, Sarny's determination, resourcefulness, and astuteness is clear from Paulsen's text. Like Nightjohn, Sarny is determined to learn how to read and write so that slaves like her can tell the world about the cruelties they have endured.

Sarny is the protagonist in Nightjohn by Gary Paulsen. She is a twelve-year-old slave who has higher aspirations for herself. Her mother is sold, leaving her motherless. There is a misconception that she is not a bright child because her speech is impacted by a birth defect which is referred to in the book as "a stuck tongue.” Some even believe she is a witch. In reality, she is a very introspective, smart child. Nightjohn, a former slave, returns to the South, and when he gives her the opportunity, she easily learns to read and write, proving her intelligence. 
As a slave, Sarny’s literacy sets her up for problems, but she is determined, showing perseverance in the face of adversity. Despite the dangers, she helps Nightjohn as he educates other slaves because she is adamant that literacy is the key to a better life for those who were enslaved.