A 48-year-old woman presents with heavy menstrual bleeding, experiencing flooding and passing clots, impacting her quality of life. She has completed her family. Examination reveals a slightly bulky, non-tender uterus. Ultrasound confirms a 3cm intramural fibroid, not impinging on the cavity, and normal endometrium. Haemoglobin is 105 g/L. According to NICE NG88, what is the most appropriate first-line pharmacological treatment to offer her for reducing heavy menstrual bleeding?