A 52-year-old woman on warfarin for atrial fibrillation (INR 8.5) presents with recurrent posterior epistaxis that has occurred three times in the past 2 weeks. She underwent anterior nasal packing 5 days ago for a previous episode, which was removed after 48 hours without rebleeding. Today, she has active bleeding from the posterior nasal cavity. Vital signs: BP 138/82, HR 92, RR 18. Hemoglobin 9.2 g/dL (baseline 13 g/dL). What is the most appropriate immediate next step in management?