I absolutely love Katie so I can understand what you mean, but right now there is no way she can become a chosen (obviously Droid can change that, but currently it can't happen).
I forget the exact conversation, but the MC mentions making her a chosen in book one, and she said it wasn't possible. I think the conversation mentioned that evokers can't be chosen because their magic and the chosen connection are too similar (someone correct me if I am wrong).
It would have made things a bit easier; I am both looking forward to, and dreading, seeing how this triangle is going to work out (mc/Katie/Emily) but right now that isn't an option.