Two years after being brutally beaten and raped, Brianna still experiences jumpy anxiety and has trouble sleeping and vivid flashbacks of her assault. Brianna is most clearly showing signs of

post-traumatic stress disorder.

Explanation:

Post-traumatic stress disorder: In abnormal psychology, the term post-traumatic stress disorder is also referred to as PTSD, and is defined as a mental illness or health condition in which an individual is triggered or affected by any stressful or terrifying event. An individual dealing with PTSD either experienced or witnessed the stressing event.

Symptoms: Severe anxiety, unstoppable thoughts, and flashbacks, etc.

Events that can lead to PTSD include sexual or physical assault, childhood abuse, serious accidents, etc.

Treatment: Psychotherapy and medication.

In the question above, Brianna is most clearly showing signs of PTSD.