Who is Isabella Van Wagenen from The Kingdom of Matthias and what is their importance?

Isabella was a former black slave turned housekeeper who became Matthews' housekeeper and one of his most loyal disciples. Though believing wholeheartedly in Matthews, she came to view his attraction to Ann as a weakness and a test of his faith. Along with Matthews, she was accused of poisoning Pierson to death, but a verdict of not guilty was rendered by the jury.