When sara returned from her tour of duty in iraq, she experienced symptoms of a posttraumatic stress disorder, which is a part of which dsm-5 category of disorders?

Those systems will be part of Anxiety Disorder.
Anxiety disorder makes a person constantly experience irrational worry even though they're not a part of any form of danger.
People who had experience in combat zone are much more likely to develop this disorder because they had to constantly worry about their life/well-being, and they couldn't leave this mindset when they returned home.