Who is Charlotte Hussey from Ahab's Wife, or, the Star-gazer: A Novel and what is their importance?

Charlotte Hussey lives in Nantucket and is an old girlfriend of Kit's. When she believes that Kit was killed at sea, she marries Mr. Hussey and helps run the Try Pots Tavern. Kit and Una live with the Husseys when they return to Nantucket, and Charlotte and Una become good friends. When Charlotte receives a letter from Kit Sparrow, she disappears from Nantucket.