You FIRED her! For checking her Facebook page!! Holy crapp!!! (i know this thread is old but I had to weigh in)

She's probably better off not working for you if you're that stingy. I can see firing her for trying to check your stuff, but not her own. All you had to do was just say, I'd rather you didn't use my computer when I'm not around, it's just my policy. Then if she blatantly disregards your request, then fire her. It's called communication! Like someone else said, maybe her previous employer(s) let her do it and she didn't think. That being said, she still should have asked. I just don't see that offence rising to the level of termination.