Final answer:
Lucy's demeanor in the conversation can be described as defensive.
Step-by-step explanation:
Based on the given information, Lucy's demeanor in the conversation can be described as defensive.
The mention of a mild stiffness and her effort to reassure the person indicate that she might be feeling defensive, either due to being disturbed or affected by the other person's nervousness.
This suggests that she is trying to protect herself or justify her actions.