The detail that helps you understand that Rosemary is a complex character is:
a. "Be frightfully nice to her. Look after her. I don't know how. We haven't talked yet. But show her-treat her-make her feel-"
This quote suggests that there are nuances to Rosemary's character that others are trying to navigate, indicating that her feelings and the way she impacts those around her are not straightforward. The instruction to treat her in a particular way hints at her vulnerability and the need for careful handling, reflecting the complexity of her character.