] I think Caroline is more likely aware that Lizzy dislikes her about as much as she dislikes Lizzy..and I think that may have been in the back of Caroline's mind when she decided to speak of Wickham to Lizzy. Caroline is counting on Lizzy not believing her and that would anger her enough to feel more sympathetic towards Wickham.

I don't give Caroline credit for quite that much cunning. I think that for Caroline, demonstrating how close she was to Darcy while at the same time crowing over this gentleman's daughter with the low connections who had the bad taste to have the son of a steward as her "favorite" would have been more than enough motivation for Caroline all by itself.

] Caroline may also hoped that Lizzy say something to or in front of Darcy that would demonstrate to him how unsuitable she would be as mistress of Pemberley.