The best answer is C. Having an unlucky number for dinner creates the conflict she faces of jeopardizing her social status.
Mrs. Pringle's reaction to having fewer guests than expected likely reflects her concerns about social appearances and the implications of an "unlucky" number of guests, which could affect her standing in her social circle. This concern about social status is a common theme in literature where characters are portrayed as being very mindful of societal expectations and the judgments of others.