To determine the character trait of the niece in H.H. Munro's "The Open Window," we should consider her actions and words in the excerpt.
Based on her ability to spin an elaborate story about her aunt's supposed tragedy and the way she interacts with Mr. Nuttel, it can be inferred that she is imaginative. She creates a compelling narrative that both captivates and misleads Mr. Nuttel.
Therefore, the correct response is:
imaginative