Who is Miss Sadie from Moon Over Manifest and what is their importance?

Miss Sadie is an immigrant from Hungary who originally came to Ellis Island with her small son. When an infection of the eye keeps Miss Sadie from being allowed in the country, Miss Sadie is forced to return to Hungary and leave her child behind. Miss Sadie returns and discovers that her son has been sent west on an orphan train and adopted by the owner of a hardware store. Miss Sadie moves to the town where her son is growing up, but she refuses to tell him who she is because she does not want the stigma of immigration to color his life. However, Miss Sadie watches from a distance as Ned grows up and grieves for his death nearly as deeply as does the young boy called Jinx.