Katarina is easy to deal with. As she normally skirts around at 50% health, having a warwick or a teemo on your team can greatly weaken her through the early game preventing her from ganking. This transfers into her being much weeker later. If you don't have either of those champions you can generally beat her by staying in at least groups of 2, and tower hugging or being in a group of three. As long as those groups have a stunner or a good slow she will not be able to gank you, again causing her to end up being late. She is able to last hit very well in the lane, but if you can get a good pusher agaisnt her she suddenly loses all of her laning prowess again ruining her entire game.