This question involved the plot of the novel and the description of the characters. Different novels might have different answers. In most novels, the mother writhes on the floor probably because she feels lonely, scared, or sad and wants comfort or companionship. It could also be that the mother wanted to express her love or longing to her father, or that she wanted to face the pain of death and loss alone. Of course, in some novels, the reason why the mother lay on the floor and twisted her body might be more complicated and profound. For example, it might represent the mother's longing for her father, her nostalgia for the past, her reflection on life, and so on. Therefore, it needed to be analyzed and understood according to the specific plot of the novel.