Is Nora a criminal?

Nora has broken the law by committing fraud. She has forged her father's signature for a loan, which is what makes her vulnerable to Krogstad's blackmailing. Her crime is a small one, but ironically, it is identical to the crime that Krogstad had committed in the past, the crime that led to his isolation from the community.
So, the simple answer to this question is yes, Nora is indeed a criminal. But the audience has to wonder if sympathy for her plight is appropriate. After all, she forges a signature years before in order to get money when her husband is ill. Her intentions are good, and her worry about her family is understandable, but her capacity for deception is not limited to just this one incident. This makes her a more complex character than any stereotypical criminal who commits fraud for personal gain.