Barbara is Billy's daughter. She is responsible for him after his injuries and Valencia's death, and the burden makes her resentful and picky. In 1968, when Billy writes his letters about Tralfamadore to the local newspaper, she is only 21, and her mother has just died of carbon monoxide poisoning. The loss of her mother, Billy's public strange stories, and her sudden huge responsibility made her an awful girl. We call such type of words with not very good words. She is really worried about Billy, but she's also incredibly disrespectful—she insists on taking over his life, making him even more powerless than he has been throughout the rest of the novel.
Barbara Pilgrim in the Essays