It must be on a patient with anxiety disorder. It can be an adult.
The development of the sections needs to show continuity between the sections and the diagnosis and plan at the end. In other words, the faculty who reads your note should be able to see your thought processes in the note while you are writing each section, and the faculty should see where you are heading with your diagnosis and plan-before arriving at those sections. It should make sense to the faculty when the faculty reviews your diagnosis and plan at the end. Refer also to Carlat for further guidance in writing your case study report.