This is Juvenile Systemic Lupus Erythematosus (JSLE)
There are features of a multisystem illness but infection and malignancy need to be excluded with blood tests (full blood count, film), acute phase reactants, autoantibodies, complement (C3,C4), thyroid function and urinalysis. She has polyarthralgia predominantly.
Investigations demonstrated features consistent with JSLE (mild lymphopenia, low C3 and C4. ANA positive and ds DNA positive). ESR was raised (35mm/hr) but CRP normal. Urinalysis was negative (.e. renal involvement unlikely).
She was started on hydroxychloroquine to help joint pain.