Final answer:
The social worker should first evaluate the client for depression due to her symptoms of feeling worthless, losing interest in activities, being inattentive, and weight loss.
Step-by-step explanation:
The social worker should evaluate the client for depression first. This initial step is critical given the presenting symptoms - feeling worthless, loss of interest in usual activities, inattentiveness, and weight loss. These signs are often indicative of depression, and understanding the client's mental health status is essential before considering further referrals for psychological testing, substance abuse assessment, or medication.
Once an evaluation for depression is completed, the social worker can better determine the most appropriate course of action, which may include collaborating with school psychologists, psychiatrists, or other mental health professionals to support the student's well-being. It's important to approach the situation with empathy, maintain a focus on the student's safety, and establish a plan for immediate and long-term support.