She could be having a "cat" day where she feels like driving you bonkers by hiding and making you worry all day.

My fat black kitty Gigolo (yes he earned the name) likes to do that. The last time after calling and calling and searching for him for what seemed like forever and finally giving up and worrying all night, I found the little brat fast asleep on my brother in law's motorcyle in the garage. I know the little so and so heard me, he just felt like being a PITA that night.