A 52-year-old Indian woman with a 10-year history of recurrent biliary colic presents with acute right upper quadrant pain, fever (39.2°C), and vomiting. On examination, she is icteric, tachycardic (HR 115/min), and hypotensive (BP 105/65 mmHg). Murphy's sign is positive. Ultrasound shows a thickened gallbladder wall (5 mm), pericholecystic fluid, multiple stones, and a sonographic Murphy's sign. Liver function tests show elevated transaminases (AST 420 U/L, ALT 380 U/L) and bilirubin (3.8 mg/dL). Blood cultures are pending. She is started on IV fluids, broad-spectrum antibiotics, and analgesia. After 6 hours of resuscitation, she remains febrile with persistent right upper quadrant tenderness. What is the most appropriate next step?