If you would look up PTSD, the symptoms are accurately written by the writers and skillfully portrayed by Beckett. If anyone says that Kate is too much of a strong character to show any weakness, well...they're simply wrong. Especially since Kate admits at the end that her weakness started with her mother's death, YEARS before she was faced with death of her own. So when those yet unsurfaced issues were triggered by this sniper case, it was more than reasonable to see her at such an emotional state.
Well Done Stana!