It could be argued that Nicola learns more from Giles than from Rowan. After the stopping the train incident Nicola has learned nothing -she still acts impulsively without thinking through her actions, - on the hike, and going to port Wade. After all, from her POV what's to learn from stopping the train - she got her knife back, she didn't get hurt and she didn't get her pocket money docked for the few years to pay for the fine. Whereas after Port Wade she seems to be a responsible and sensible girl - often the person who points out to other people the flaws in their plans or tells other people not to be silly about things. So if an officer's role is to train their juniors I think Giles has done better than Rowan.