PLE-2740

A 15-year-old girl is brought to the emergency department by her 20-year-old sister because of a 1-week history of fatigue, nausea, and abdominal pain. Menarche was at the age of 12 years, and her last menstrual period was 3 weeks ago. She has not had vaginal discharge. She is sexually active, and she and her partner use condoms inconsistently. Her temperature is 37°C (98.6°F), blood pressure is 110/60 mm Hg, and pulse is 95/min. Abdominal examination shows mild bilateral lower quadrant tenderness. Before a pelvic examination and a pregnancy test can be performed in this patient, consent must be obtained from which of the following?