Who is Mrs. Hanrahan from The River Between Us and what is their importance?

Mrs. Hanrahan is the wealthy woman with whom Delphine and Tilly make their temporary home, while traveling to Cairo to retrieve Noah. The observant, sharp-tongued, and racist Mrs. Hanrahan concludes that Delphine has black ancestry almost as soon as the two women meet, and her confrontation with Delphine on the subject triggers realizations in Tilly that her friend is not what she believed her to be.