What Is this rubish about depression. Yes she may be a bit down but it certainly doesn't sound bad enough to be a complete insensitive arse. You don't tend to loose the very core of your personality until it gets very severe. I mean institutionalised bad.
Thing is you never know what's going on in someone elses head. This girl I was talking about, god...... there's a lot happening there. It's easy to sit on the outside and judge but far more helpful to try and help someone who's having a hard time of things.