A 27-yeаr-оld wоmаn presents 10 dаys after being invоlved in a serious motor vehicle collision in which a passenger was critically injured. Since the accident, she reports recurrent intrusive memories, trauma-related nightmares, intense distress when hearing screeching tires, inability to feel happiness, episodes in which her surroundings feel unreal, avoidance of thinking about the accident, avoidance of driving, difficulty sleeping, and hypervigilance. She has missed several days of work because of her symptoms. She denies substance use. Which diagnosis is most appropriate?