A 32-year-old woman with a history of PID presents with acute lower abdominal pain, fever (39.2°C), and a palpable adnexal mass. She has been on oral ceftriaxone and doxycycline for 3 days with no clinical improvement. Transvaginal ultrasound shows a 6 cm complex adnexal mass with internal echoes consistent with a tubo-ovarian abscess (TOA). What is the most appropriate next step in management?