KR going into panic mode at 4:40 AM does not and will not compute.
She knew/remembered something had happened. There's no mass-conspiracy that can explain that away.
Why? I know a lot of people who would panic if they woke up at 4 AM and their partner hadn't returned home. And I know others who would probably just roll over and go back to sleep.
I have no idea which group Karen falls into, but I don't see her reaction as some kind of smoking gun. At least not without knowing more about her relationship with JO. Had he ever stayed out all night before? Was he generally a reliable person? Does she have anxiety? And so on.