Darcy, on the contrary, had seen a collection of people in whom there was little beauty and no fashion, for none of whom he had felt the smallest interest, and from none received either attention or pleasure. (Chapter 4)

Caroline is Darcy’s faithful assistant; she appears to be just defending him as she did in all their little discussions at Netherfield. Aside from this rather predictable partisan behavior she also does not know the circumstances between Darcy and Wickham. Caroline’s guilt and descent argument has no merit; especially to Lizzy who along with the rest of Meryton was guilty by the same reasoning and treated accordingly by Darcy in Chapter 3. To me it is only good sense that Lizzy ignores Caroline’s prejudiced and unjust advice. I think if Caroline had been Lizzy’s intimate friend she would have felt the same about her advice but would have been nicer in the way of dismissing it. Lizzy also ignores Bingley’s account of what happened and even Jane’s reasoning in Chapter 17 so friendship, even when intimate did not lessen her faith in Wickham. ;D