A 15-year-old girl presents to the outpatient clinic with a 2-year history of headache episodes which have been getting worse for the past six months. For the last two months she has been suffering daily headaches for which she takes regular 500mg paracetamol 3-4 times daily and 200mg ibuprofen 2・3 times daily. Six weeks ago she was admitted to hospital overnight and given oramorph, which fully relieved her headache for a period of 12 hours. MRI head during that admission was normal. There is a family history of cyclical vomiting syndrome and migraine with aura. On examination she weighs 67kg, has a BP of 115/68, and the systemic and neurological examination is unremarkable.What is the most appropriate next step in the management?