A 70-year-old woman is found to have new-onset non-valvular atrial fibrillation during a routine visit. She has no history of hypertension, diabetes, heart failure, prior stroke, or vascular disease. Echocardiography is normal and there is no valvular pathology. According to the Canadian Cardiovascular Society CHADS-65 algorithm, what is the most appropriate antithrombotic strategy for stroke prevention?