How could the submissive selfish and silly Nora of the first two acts transform herself into an independent woman by the end of the last act?

In the course of the play, Nora undergoes a profound transformation as she confronts the realities of her marriage and her own identity. By recognizing her role as a mere puppet in her husband's life, she gains clarity about her desires and the constraints placed upon her. This awakening drives her to assert her independence, culminating in her decision to leave Torvald and seek her own path. Ultimately, Nora's journey reflects her rejection of societal expectations and her commitment to personal growth and self-discovery.