A 64-year-old woman is admitted to the medical ward presenting with a 4-day history of escalating fever, profound dizziness, and recurrent vomiting. She reports inability to tolerate oral intake and persistent temperatures exceeding 38.5°C despite home remedies. Accompanying symptoms include generalized malaise, rhinorrhea, nasal congestion, and a mild, non-productive cough. Her medical history includes well-controlled essential hypertension. On examination, she appears acutely ill and lethargic. Her vital signs are notable for a blood pressure of 90/60 mm Hg, a pulse rate of 118 beats/min, respiratory rate of 20 breaths/min, and an oral temperature of 39.1°C. Physical examination reveals dry mucous membranes, reduced skin turgor, and a capillary refill time of 4 seconds. Cardiopulmonary auscultation is unremarkable save for the regular, rapid heart rate. Rapid molecular testing for respiratory pathogens confirms the presence of influenza A virus. Considering her current clinical state, what is the most appropriate initial diagnosis and subsequent management plan?