Does my mother have dementia?

My mother is 72 and she had a PRP operation to her knees back in December. 1 week after the operation she started showing symptoms for delirium. Later we found out that she had not slept for 10 days before she completely lost it and called cops to the house claiming that there was somebody in my sister's room, which was not the reality. We managed to take her to the hospital where doctors found urinary track infection and border line blood sugar levels. She stayed in the hospital for 5 days and received heavy doses of antibiotics. Doctors also told her not to eat sugar anymore. She has been good until the last week since January after she received the treatment. She said she ate very heavy desert, which may have spiked her blood sugar. But this time her blood results and sugar levels ook normal as well as brain MRI. One thing that is not normal this time is that she just sits for hours and day dreams. Once in a while she tells me that so and so said hi to you. In her head she is talking to people. These people actually exist in real life but she is talking to them in her head. Yesterday she came running from the kitchen to look outside and said your father's friend is here. Both my father and his friend are long gone. When i told her what she was experiencing was not real she got upset. Aside from all the weird things she does now the most concerning to me is the sitting for hours in withdrawal with her lips moving and rapid blinking. Unless I ask her questions she does not engage in conversations. Even when she speaks sometimes she goes back to day dreaming in mid sentence. Doctors said she does not show signs of dementia after talking to her for 45 minutes to assess her speech and cognitive skills but based on what I have been reading these are signs of a type of dementia. Anyone experienced similar symptoms with elderly loved ones?