For all i can praise regarding GTA 4 and it's writing, Kate is not part of that. They tried to portray her as the innocent one that's unfairly affected by the shit all the people around her drag in, but she's so condescendingly righteous about it that it's a real put off. That would've been understandable if you were playing as Claude or Tommy Vercetti, who are the sociopathic monsters she bitches about, but with a character much more layered like Niko, her constant "So, how's your expendable life as a dumb brute going?" monologuing gets frustrating, all the more because Niko never really calls her out on it.