First, I'd probably say, "hey, what was with the phonecall?" If she responds honestly, I might ignore it, severity of the situation depending. If she blatantly and obviously lies about it, I might respond by saying, "I think I should take you home now." When we got out to the parking lot, I might say something like, "I left something important in the trunk," crack her over the skull with a tireiron, stomp her cranium into a spongy sludge, and back over her corpse as I peel the fuck out, masturbating and laughing maniacally.