A 62-year-old postmenopausal woman presents with a T-score of −2.8 on DEXA scan of the lumbar spine. She has no prior fragility fractures, no contraindications to bisphosphonates, and normal renal function (eGFR 78 mL/min/1.73 m²). She is currently on calcium 1000 mg and vitamin D 800 IU daily. What is the most appropriate next step in management?