You always want Crowd Diver Chosen Katarina to open up the 6 Crowd Diver late game win condition. I would not recommend taking Country Chosen, as this trait won't provide anything meaningful for her. You want to finish a quick Katarina*3 with Level 6 and push towards Level 8/9 to include more Crowd Divers.
In late game you have great additional carries with Zed and Qiyana who are more than capable of carrying an fight by themselves as well. Keep in mind that the Crowd Diver trait is less about their jump into the enemy backline and more about their built in damage scaling the longer the fight goes. This is why you have to prioritize sustain items and keep your carries alive, because the longer the fight, the better for you!