A 28-year-old woman from rural Maharashtra presents with a 3-day history of severe sore throat, fever (39.5°C), and difficulty swallowing. On examination, she has bilateral exudative pharyngitis with enlarged tonsils, petechial rash on the soft palate, and tender cervical lymphadenopathy. A rapid antigen detection test (RADT) for Group A Streptococcus is positive. She has no history of penicillin allergy. Which of the following is the most appropriate antibiotic therapy?