The rest of the passage in the book says, "... Georgiana also recovered in time, though not enough to be able to speak any more. Her brother, whose eye she feared to meet, scarcely recollected her interest in the affair; and the very circumstance which had been designed to turn his thoughts from Elizabeth, seemed to have fixed them on her more, and more cheerfully."

I think that Darcy was unsure of whether Elizabeth still had fond feelings for Wickham, unsure of whether she had believed what he (Darcy) had written in his letter. Caroline has tapped into that insecurity by asking this question. When Elizabeth reacted (relatively) calm, cool, and collected, however, Darcy felt relief and was able to enjoy the rest of Elizabeth's visit. He was not really thinking about Georgiana's escape from Wickham during this point in the conversation.