Who is Clara Glencairn de Figueroa, Marta Pizarro- The Duel from Collected Fictions and what is their importance?

Clara Glencairn de Figueroa was the wife of the Argentine ambassador to Canada. After her husband's death, Clara chose to start a career as a painter. She is assisted in her endeavor by her friend and occasional rival, Marta Pizarro, who is also a painter. After Clara's death, Marta paints Clara's portrait, and never paints again.