An 86-year-old woman is recovering from surgery for a hip fracture that she sustained in a fall. She has been receiving antibiotics and occasional narcotic medications for pain but is on no other medications. Her family requested psychiatric evaluation as “she seems depressed” and was asking unusual questions such as “When did they start letting dogs come into the hospital?” This was upsetting to them as she had been independent at home and taking care of her own finances prior to admission. On mental status examination, she seems subdued and slow in her responses but says her mood is “OK, I guess.” Although she needed to be redirected multiple times while assessing her cognition, she was oriented in all spheres and able to recall 2 of 3 items at 3 minutes but had difficulty spelling the word WORLD backwards. Her score on the Mini-Mental State Examination was 24/30. Which of the following diagnoses is most likely?