Bergman's Nora is not merely a flighty, chirpy songbird who inhibits Helmer's cage, although she does play that role, but "a woman of under terrible stress" filled with a sense of being unsatisfied...
As the play progress, Nora's illusions, and her ability to live in them, come under more and more pressure, until in the penultimate scene, her husband destroys her most sustaining illusion, that he will be grateful to her for saving his life.