Nora's character strengths include her dedication to the men in her life (father/husband), her innocence and naivete, the ability to make people around her smile, and her loyalty and love for her friends, and her children.
Her weaknesess are plenty: She has neglected herself, lives in a fantasy world, assigned herself a fictitious role as her husband's doll/squirrel/lark or whatever name he chooses to give her, she acts impulsively, is very immature, and does not recognize consequences for her actions.
Both her weaknesses and strength make Nora who she is: A woman lost. She has no clue what she wants from life or what to expect from people except from what her imagination dictated her due to her immaturity, her lack of exposure to the real world, and her naivete.
For this reason, when Nora faces for the first time the cruelty of reality through her husband's reproach, all that she had built came down to shambles. She had built a reality based on her weaknesses, and her strengths were openly rebutted by the man she sacrificed her dignity for: Her own husband. She then decides to walk away, although not knowing where to. All that we know is that Nora finally woke up and chose to face life the hard way, perhaps as a way to make herself learn.