A 20-year-old woman presents with a 2-week history of dysuria, urinary frequency, and urgency. A mid-stream urine (MSU) sample shows >10^5 cfu/mL of E. coli, sensitive to trimethoprim, nitrofurantoin, and ciprofloxacin. She has no known drug allergies. She is not pregnant. According to NICE NG109, what is the most appropriate first-line antibiotic treatment for this uncomplicated lower UTI?