Final answer:
The nurse should recognize difficulty concentrating and irritability as signs of PTSD, an anxiety disorder common after trauma, which includes symptoms like flashbacks, avoidance, and heightened arousal.
Step-by-step explanation:
The school nurse should identify difficulty concentrating and irritability as indicators that the child may be experiencing post-traumatic stress disorder (PTSD) after the traumatic loss of a parent. PTSD is an anxiety disorder that can develop following exposure to a traumatic event. Difficulty concentrating and irritability are among the common symptoms, along with other possible symptoms like re-experiencing the trauma through flashbacks or nightmares, avoidance of reminders of the trauma, and heightened arousal leading to sleep disturbances or a heightened startle response.