Who is the Elk Spirit from the novel, The Only Good Indians?

The one character whose presence is consistent throughout the novel (although in different incarnations) is a vengeful elk spirit. Its exact nature and origins are mysterious, but it seems to be the spirit of one (or multiple) of the elk that the hunting group illegally shot. The main narrative takes place ten years after this hunting incident, and the elk spirit is determined to take revenge against the hunters: Ricky, Lewis, Cassidy, and Gabe. The spirit takes various incarnations, such as a human woman, and an elk-headed woman.