I thought the same thing regarding "Mrs. Leaver". Based on the excellent English used in the letter, Mary Touzeau would seem to have been thoroughly English, despite her very French-sounding name. Roland Touzeau (born 1766) appears to have had a sister named Susan le Lievre Touzeau (1779-1820) so it makes sense that Mary may have anglicized the name. On the other hand, she appears to have been fairly well educated based on the fact that she obviously could read and write well (unless, perhaps, she dictated the letter to another).