Who is Baroness Theresa de Stolberg from Wieland; and Memoirs of Carwin the Biloquist and what is their importance?

Baroness Theresa de Stolberg was Pleyel's lover. She later became his wife. Over the course of the story, Theresa fakes her own death in order to join Pleyel in America. Her scheme misfires, however, when Pleyel receives word of her death before she arrives.