Your first step in completing this assignment is to determine which characteristic of Nora in A Doll's House you would like to focus on for your description. Nora has both positive and negative traits, and you could go either way depending on how you have responded to her. Let's look at some options.
If you choose to take a positive view of Nora's character, you might focus on her courage. Nora does what she must to help her husband, Torvald, regain his health. In her case, that actually means doing something technically illegal. As a woman, she cannot take out a loan in her own name, yet she desperately needs the money to take Torvald to Italy. So she forges her father's name on the loan. This is illegal, but we have to question if it is really unethical. Nora makes up her mind that it is not, and she goes ahead with it. Then she works hard to pay the loan off so as not to bother her husband about it. In using a quote to support this, you might look at the part of the play in which Nora is explaining the situation and her motivations to Mrs. Linde.
Yet there is another side to Nora as well. Nora does lie about where she gets the money. She keeps secrets from her husband, and this is, at the very least, tricky. In fact, it nearly backfires on Nora and nearly exposes both her and her husband to social shame when Krogstad threatens to go public with Nora's forgery. Nora is now in a tight spot. If she had already told her husband about the loan, he could have headed off this problem early on. That said, though, we can see why Nora doesn't tell him. When Torvald finds out about the loan and its consequences, he turns quite nasty toward Nora, telling her that she has “destroyed all [his] happiness” and “ruined all [his] future.”
You might also think about the end of the play, when Nora determines to leave her husband and children. Some may think this shows a weakness in her character, as she seemingly resolves to abandon her children.