Welcome Mumandme. Glad you decided to come join us. From you lurking you know it's a great group. Drag up a chair, grab a glass of wine, and stay a while. Oh, and here's your first towel
I think my Mom is in her fourth year, two years since her diagnosis. Her's has been a slow decline and most days she still manages ok in AL. If strong will has anything to do with it, her will to care for Dad has kept her going. He is about 9 years into Vascular dementia. He has had a few step downs (which is typical of vascular dementia) but for the most part maintains the status quo.
My grandmother did as you described with your Mom but it was a result of a massive blood infection and long stay in the hospital. She never recovered her previous level of cognitive awareness. She went from home with a live in care giver, to the hospital, and then spent a year bed ridden in a nursing home.
I do know each loved one progresses differently. I am sure they have done a urinalysis to check for a UTI. How old is your Mom? I am truly sorry you are having to deal with this. I do hope you find answers to your questions.
I will keep you and your Mom in my thoughts and prayers......