The most appropriate response that highlights the effects of dramatic irony in the passage is:
Readers understand why Rebecca tries to divert Captain Barrington by saying she is mending the overcoat for a townsman in need.
This response illustrates how the audience is aware of Rebecca's true intentions—her efforts to distract Captain Barrington and protect the messages for the Continental Army—while he remains oblivious to her actions. This creates a sense of dramatic irony, as readers can see the tension between Rebecca's actions and her underlying motives.