Who is Mrs. Rees from The Ruby in the Smoke and what is their importance?

Mrs. Rees, a distant relation, takes care of Sally after her father's death. She is mean to Sally, and she constantly accuses Sally of taking advantage of her 'charity.' What Sally doesn't know is that Mrs. Rees has actually been accepting Sally's income on her own behalf. When Sally discovers this, she is both shocked and annoyed, and quickly makes sure that all money will come directly to her in future.