No, Kate is not a girl. Kate is a text editor. It comes with KDE by default, but unfortunately not with GNOME (probably because it is a KDE program). I've noticed that I really prefer the set of KDE apps to a lot of their GNOME equivalents. Kolourpaint is much better than gPaint, KDevelop is better than Anjuta, and I like KPDF as the default PDF file viewer. Unfortunately I don't like the amount of options given by KDE, so GNOME stays. I do think though that KDE is better for beginners, as it looks nicer and I think it is easier to use. GNOME has a bit of a boring look to it.
So now to Kate. Why is it awesome? It just is. There is syntax highlighting, intelligent indenting and support for a lot more languages than with Gedit (like bison grammars). It keeps all your open documents in a vertical, hideable list on the side. If I have over 20 documents open, the clutter is about the same as if I have one document open. With Gedit for example, I can have about 5 documents open before I have too many tabs to fit on the screen. With a vertical bar, I can just click the one I want to switch to.
Kate lets you configure it more. I don't like the default shortcuts for changing the current document, so I put it to the way Firefox switches tabs: Ctrl+Tab and Ctrl+Shift+Tab. Hooray! Much easier than what was there before. There are also lots of plugins out there, so I have things like code-folding and bracket-matching. Awesome. What finally takes the cake is that the highlighting schemes and all that are shared between KDE apps. So KDevelop and Quanta will have my code look the same as Kate does. That way if I have a tiny change to make, I can just open Kate instead of an IDE and that takes a lot less time.