Who is Nicole / Dao from The Tears of Autumn and what is their importance?

Nicole / Dao is a young Vietnamese woman living with the Truon toc of the Ngo family in Saigon, Nicole (her French name) is initially hostile towards the American Paul Christopher, who discovers that in September 1963, she is the mystery woman seen in Bangkok with a North Vietnamese official, Do Minh Kha. She is sent to tell her long estranged biological father of the family's plan to assassinate John F. Kennedy in retribution for killing Ngo Dinh Diem and Ngo Dinh Nhu. Do goes on to talk with a Cuban agent, Manuel Ruiz, who handles connections with Lee Harvey Oswald.