Caroline Bingley's criticisms of Elizabeth never help Caroline win Darcy in any way. Instead, they actually serve to show Darcy just how conceited Caroline really is. One instance of criticism takes place after Elizabeth walks three miles through mud to get to Jane at Netherfield. Caroline remarks on the condition of Elizabeth's skirts and her hair. Though Darcy agrees that he would not ever want his young sister doing the same, when Caroline suggests that Elizabeth's appearance made him think less of Elizabeth's "fine eyes," he very coolly replies "Not at all...they were brightened by the exercise" (Ch. 8, Vol. 1). His cool reply shows that he probably agrees more with Bingley, that Elizabeth's actions show how fond she is of her sister, than with Caroline's criticisms.
A second instance Caroline's criticisms of Elizabeth are met with coolness from Darcy takes place when Elizabeth is invited to dine at Pemberley. Caroline insults and criticizes Elizabeth's looks and Mr. Darcy replies that she is "one of the handsomest women of [his] acquaintance" and leaves the room (Ch. 3, Vol. 3). Again, Caroline was trying to use criticism to dissuade Darcy from being attracted to Elizabeth, but again her criticisms only serve to prove how ill-mannered Caroline is and confirm Darcy's admiration for Elizabeth.