Who is Sylvia Du Vrais Zetterling from God Bless You, Mr. Rosewater, or, Pearls Before Swine and what is their importance?

Sylvia is the wife of Eliot Rosewater. She is from Paris and a descendant of the Rothschilds and DuPonts. She hates Eliot and is divorcing him and sends Mushari fifty-three letters when he requestes any letters she might have.