I think Arya's ark is BS. She spent years breaking herself down psychologically, reprogrammed herself to be a nameless cold blooded killer, only to become scared little Arya Stark in crucial moments. Yet she keeps falling upwards.
Btw, it seems to me that being a veteran in the battle against the army of the undead is a more stressful and PTSD-inducing experience. The northerners and dothraki sacking, pillaging and raping their way through King's Landing just seems like appropriate behavior for the time period.