It's a great fault because there is an unnatural unaccounted for jump in her development.
People need reasons for what they do.
Tomino doesn't always state those reasons explicitly and he often has his characters do random things for seemingly inexplicable reasons though unlike with Katejina I am usually able to deduce those reasons with at least some level of certainty from the context. I complained about it earlier but in fact that is what makes his writing good. Real people are not easy to understand. Real people don't have sympathy invoking sad flashbacks and they don't turn to the camera to tell you how they feel on the background of sad violin music so you can sympathize with them. If that is what you mean by "you can never pin her down" then I agree.
But is you mean that she is just bad and not "meant" to be understood and thus you are excused from trying to understand her then I can't agree with you on any of those points.