A 72-year-old woman with a history of mitral stenosis and atrial fibrillation for 8 years presents with acute-onset severe dyspnea and hemoptysis. On examination, she is hypoxic (SpO₂ 88% on room air), tachycardic (HR 160/min, irregularly irregular), and has bilateral basal crackles. BP is 100/60 mmHg. ECG confirms AF with rapid ventricular response. Chest X-ray shows pulmonary edema. Echocardiography shows severely dilated left atrium (6.5 cm), mitral valve area 1.2 cm², and reduced LV ejection fraction (35%). What is the most appropriate immediate management?