Even though the play begins with a seemingly merry Christmas scene, the scene is far from ideal. Torvald's treatment of Nora is patronizing and controlling. He calls her "lark," "little squirrel." When she wants to show him what she bought, he calls her his wasteful "little spendthrift." In short, he treats her like a child, doling out money, admonishing her not to waste it, even scolding her about eating macaroons.
Later we learn that Nora has more depth than we originally thought. She secretly (and illegally) borrowed money for a vacation that she believed would save Torvald's life, knowing that she risked his disapproval with this venture. She has been also secretly doing work on the side to repay this loan. Nora is further aware that Torvald might some day grow tired of her when she is not as young and cute as she is now. She tells Mrs. Linde that she is preparing for the day when "Torvald is not longer as devoted to me as he is now; when my dancing and dressing-up and reciting have palled on him." So, even though Nora may act like a child, she is a woman who is very aware of her actions and can make decisions on her own.
What Nora, though, learns through the course of the play is that Torvald cannot accept her as the woman she is. He is furious when he finds out that she borrowed money. He says he will not sacrifice his honor for his love. When she tries to explain to him why she did what she did, he tells her that she is speaking like a child. Nora then reminds him that she has always been like a child to him, that they have never really discussed matters as equal.s
Nora's realization that their marriage is not the "wonderful" she thought it was, that she has sorely misjudged her husband, who will never see her as the adult she is, and that he in turn has misjudged her is the crux of the play. I think she was always an adult, but she played a child's role. When she demands that she be treated as the adult she is, the marriage becomes unstable, and she exits.