Juvenile idiopathic arthritis (JIA) represents a diverse group of arthropathies affecting individuals under the age of sixteen. Enthesitis-Related Arthritis (ERA) is a subtype of JIA that primarily affects the lower extremity joints and entheses and is often associated with HLA-B27 positivity. We present the case of a 17-year-old female with a history of tuberculosis who presented with fever and arthritis and was initially misdiagnosed with septic arthritis. Despite an escalation of antibiotics, the patient showed no improvement. Subsequent investigations, including imaging and synovial fluid analysis, ruled out infectious aetiologies. The patient was ultimately diagnosed with ERA based on the clinical, laboratory, and imaging findings. Treatment with NSAIDs and methotrexate resulted in symptomatic improvement. This case highlights the diagnostic challenges in distinguishing ERA from septic arthritis and underscores the importance of a thorough diagnostic approach in similar clinical scenarios.