Mom was just a couple months shy of 94 when she died, and I think you need to expect some mental deterioration at that age in most cases, but in my opinion the mental deterioration had been going on for at least 15 years.

My brother says 11 years, but he saw her every day, which I think made it more difficult to recognize the small changes that started occurring years earlier. I live much further away and often didn't see her for several months at a time, so it was a lot more difficult for me to "explain away" the changes that I saw from one visit to the next.

It wasn't that she was refusing to heat a good diet - it was the definition she'd been convinced constituted a healthy diet, which as her mental ability started to go, she did as you said and wanted more and more sugar (and starch - since that converts to glucose even faster than sugar) just to keep herself going throughout the day. I can certainly identify with that from my decades on a low fat, minimal protein, "heart healthy diet" - I was utterly exhausted all the time, while constantly giving in to cravings for sweets and starches.