A 28-year-old woman from Jharkhand is diagnosed with *Plasmodium vivax* malaria (parasitaemia 0.8%) on day 2 of fever. She is started on chloroquine 600 mg base stat, then 300 mg at 6 hours, 24 hours, and 48 hours. On day 10, she remains fever-free and asymptomatic. What is the most appropriate next step to prevent relapse?