[ her face doesn't have to say it - her words do too. elena notices, either way. she has no argument about it, knows caroline has every reason not to trust rebekah. (and so does elena.) yet it gives her some pause - she hadn't even considered rebekah might lie about that. she had no discernable reason to lie.
she lets the moment pass because she'd rather not think about caroline's dislike for rebekah. or maybe she'd rather not think about her own feelings towards rebekah lately.
anyway, speaking of friends and what's really important at the moment: ] Have you seen Bonnie? We've been trying to find you.