Who is Sarah Wyatt from Jailbird and what is their importance?

Sarah is the fourth of the women Starbuck says he loved in his life, and is the least developed (as a character) of his three so-called "romantic" loves (for his mother, who is never very well developed as a character, he had a different kind of love - idealized, childlike, and remote). Like Mary Kathleen, Sarah appears in two incarnations - first, as the aristocratic, impoverished, sexually frigid but proper girl with whom Starbuck gets involved when he first arrives in New York, and then later as the hard working, compassionate, idealistic wife of Starbuck's former colleague (and former "victim"), Leland Clewes.