Final answer:
The nurse is worried about the negative consequences of John's public display of emotion. She attempts to remedy the situation by calming him down and encouraging him to restrain his emotions.
Step-by-step explanation:
John’s grief upsets the nurse because she is worried about the negative consequences that may arise from his public display of emotion. She is concerned that it may worsen the mental health condition of the narrator, who is already suffering from nervous troubles. To remedy the situation, the nurse attempts to calm John down and encourage him to restrain his emotions in order to maintain a sense of stability and prevent any further harm to the narrator's mental well-being.