The word appears 2 times.
The novel takes place in Georgia... so what do you expect?
Since the people of this town don't have much in the way of interaction with Black people the word does not have that much occasion to come to hand. But when there is an interaction, it just comes naturally. Understandable given the time period of the novel.
Well, YOU could, I reckon. Being' who your are. Yore grandaddy'll give you good terms, and he ain't go'n charge you double when you send a nigger to town to git sugar and coffee on credit.
What little hair she had was damp and standin' out like a scairt cat's. Her mouth dropped open and her eyes stared straight at me. I could a-kilt that nigger woman, showin' off like that, tryin' to scare me. I backed out of theat room, I tell you.