A 68-year-old woman is diagnosed with osteoporosis following a DEXA scan (T-score -2.8 at the hip). She has no history of fragility fractures. Her renal function is normal (eGFR > 60 mL/min/1.73m²), and serum calcium and vitamin D levels are adequate after correction. According to NICE guidelines, what is the most appropriate first-line pharmacological treatment?