It's entirely possible that you simply missed cues. In Nadia's case, her character has a built in flaw that's integral to the plot and diametrically opposed to her overt confident personality. It's not unfeasible for an orphan to express illogical and destructive tendencies in tell relationships with those closest to them, and is not a coincidence that Nadia becomes more eratic the closer Jean gets to her. Still, that's not to say the compressed nature of the story contributes to the jarring sight of her abusing Jean out of nowhere. A good deal of the time, what appears to be illogical character behavior is a product of plotting.