Rubella

A 9-year-old partially vaccinated girl presents with a 1-day history of a mild rash that began on her face and is spreading to her trunk. She reports a brief prodrome with low-grade fever (38.2°C), mild sore throat, and headache. On examination, she is well-appearing and afebrile. The rash shown in the diagram at **A** is described as discrete fine pink maculopapules that do not coalesce, beginning on the face and neck and spreading cephalocaudally. The most distinctive clinical finding is prominent, tender, indurated lymphadenopathy behind the ears, at the back of the head, and along the posterior cervical chain. Based on this presentation and the characteristic lymphadenopathy pattern marked **A**, what is the most likely diagnosis?