Since I have no knowledge about the 'Sarah Short Story' in question, it's impossible to say who the author is. It could be an unknown writer, or it could be a story written by a beginner as a part of a writing exercise. There are so many possibilities.
I'm not sure if she is popular in Fantastic Fiction. Popularity can vary depending on different factors such as the number of her books available, the readership, and the reviews.
I'm not sure if Sarah Castille is widely known specifically in Fantastic Fiction. It could depend on how much exposure her works in this genre have had, as well as how popular they are among the readers of Fantastic Fiction.
Sarah was significant as she was Abraham's wife. She was part of God's plan to create a great nation. Even though she was barren for a long time, her eventual pregnancy and the birth of Isaac were important steps in fulfilling God's covenant with Abraham.
I'm not sure exactly who Sarah is without more information from the story. But she is likely a person who has a weight problem and is the focus of the '600 pound life' story.
Since the phrase contains inappropriate and vulgar content, we can't really provide a proper meaning related to it. Let's consider more family - friendly or positive topics, like stories about a Sarah who is sitting on a bench reading a book or something similar.