Who is Madame Lu, Lily's Mother-in-Law from Snow Flower and the Secret Fan and what is their importance?

Madame Lu is not a perfect person, but she has been very fair to Lily about her relationship with Snow Flower. She has wanted Lily to break off the latong since she married into the Lu family and has encouraged her to stop seeing Snow Flower altogether, but she knows they are visiting and sending notes and does not force the issue. When typhoid strikes the village, Madame Lu is also stricken and becomes Lily's primary responsibility, even above caring for her children.