The conversation between Mrs. Linde and Nora affects the plot because D. It has a major impact, because it hints at the doctor's feelings for Nora and her attempt at manipulation.
In the text, Mrs. Linde suspects of Dr. Rank's intentions with Nora, and eventually warns her about her relationship with him. But Nora pretends he is not more important than just Helmer's Doctor, and tries to deviate the focus towards Helmer's jealously.