Ah, sweet Caroline (and I am being ironic)! Yes, she's showing a bit of bossiness here, commanding Jane to rescue her and Louisa from boredom. I am sure she thinks she is being very clever in her comments about how a tete a tete between two women is sure to end in a quarrel. Obviously she and Louisa aren't as close as Lizzy and Jane are, and she can't conceive of enjoying a day in her sister's company without the diversion of the gentlemen. I think she adds the line about the men's whereabouts just as an explanation of why she and Louisa are all alone, poor things. But she could also be letting Jane know that her brother has nothing to do with the invitation, and in fact, Caroline may not ever have intended to let her brother know about it.