A 74-year-old woman presents with new-onset atrial fibrillation detected on ECG during evaluation of palpitations. She has hypertension and type 2 diabetes but no history of stroke, TIA or valvular disease. Her CHA₂DS₂-VASc score is 4. She weighs 70 kg and has an eGFR of 65 mL/min/1.73 m². What is the most appropriate long-term antithrombotic strategy to reduce her stroke risk?