Nyx? Well, she will destroy the defenses of your Kana, and also make her a little blind, but if that´s not a problem, go ahead. Now, if you are just talking about optimization, i would say that Camilla is a very nice mother in your situation, she doesn´t destroy her magic, and gives good speed, defenses, resistance, and, well, everything, she is very well rounded (no pun intended)