Who is Mrs. Andrea Curtin from Tears of the Giraffe and what is their importance?

Mrs. Andrea Curtin is an American who becomes a client of Mma Ramotswe. Her husband had been an economist with the World Bank and had accepted an assignment in Botswana ten years earlier. Mrs. Curtin and her son Michael, then eighteen, had come to Botswana with him. Michael became involved with a German named Burkhardt who formed an agricultural commune in Molepolole. When the Curtins returned to America, Michael refused to go with them, saying that his work at the commune was too important. One day, the Curtins are notified by the Embassy that Michael is missing.