Who is Jiang Weiyhe from Death of a Red Heroine and what is their importance?

Jiang Weiyhe is an artist who is a former lover of Wu. Jiang tells the detectives about Wu's collection of obscene photographs, which led to her breaking off their relationship. Jiang is instrumental in steering the investigation to its end. She has an artistic temperament that is at odds with the typical behaviors expected by the Party. She is suspicious of authority but as an acquaintance of Chen's is willing to speak to Detective Yu.