A 71-year-old woman is brought to the ER by her family, who state that she is not acting like herself. They say that several hours ago she began to slur her words as she started wandering around the house. They heard her calling to her husband, who has been deceased for over 10 years. After several minutes of this, she said she wasn't feeling well and laid down on the sofa; she then became sleepy. When they tried to ask her what was wrong, she snapped at them.

Although the woman is retired, she is very active in her church and senior citizens club. Her past medical history is significant for 3 vaginal deliveries, 10 years of hypertension, and 5 years of type-2 diabetes. She does not smoke, drink alcohol, or take drugs. Review of systems reveals that she had mentioned to her daughter the day before that urinating is painful and that her back is sore.

On exam, you find an elderly woman who is lethargic. You have to speak loudly for her to answer questions. She is alert to person but not place or time. Her vital signs and exam of the head, heart, lungs, and abdomen are all normal. She is tender at the costal angle on the right.

What is the most likely cause of her mental status change?
A. Psychotic reaction to major depression
B. Delirium
C. Dementia