Final answer:
b) She's offering help to a stranger. Katherine wants to convey a farewell message to Mrs. Harvey and leaves a note for her. She doesn't want to convey a secret or offer help to a stranger, as seen from Nora's reaction. Katherine also intends to convey a message through an item in the future.
Step-by-step explanation:
The message that Katherine wants to convey to someone can be inferred from the given texts. In the first text, she writes a note to Mrs. Harvey, indicating that she is leaving and asking her to keep something until she hears from her. This suggests that Katherine is trying to convey a farewell message to Mrs. Harvey. In the second text, Nora refuses help from a stranger, indicating that she does not want to convey a secret or offer help to a stranger. In the third text, Katherine asks the person to open something when she writes to them in the future, suggesting that she wants to convey a message through that item.