Final answer:
Keegan likely suffers from posttraumatic stress disorder (PTSD), as indicated by her symptoms, which are consistent with the diagnostic criteria for PTSD.
Step-by-step explanation:
Based on the symptoms described - inability to stop thinking about the traumatic event, heightened irritability, startled response to loud noises, and avoidance of places that trigger memories of the event - Keegan likely suffers from posttraumatic stress disorder (PTSD). PTSD is characterized by intrusive and distressing memories of a traumatic event, negative alterations in mood and cognition, hyperarousal, and efforts to avoid trauma-related stimuli. In Keegan's case, the shooting during an armed robbery is the traumatic event that has led to her current psychological and emotional challenges, consistent with the criteria defined by the American Psychiatric Association for PTSD.