Who is Delphine Blyth Sieverance from The Blue Afternoon: A Novel and what is their importance?

Delphine Blyth Sieverance was born about 1870 in America. Her early life is not fully described in the book, though she is orphaned at a young age is grows up in some penury. Delphine is described as attractive with reddish hair, very fair skin, freckled shoulders, and an English nose.