My mom received the official diagnosis of Alzheimer's and mixed dementia with vascular disease. What does this mean?

So as many of you might know from reading my previous posts, I am in charge of my Mom since April of 2016 when her husband (my stepdad) passed away. We had a trial period where she lived in our home, but that didn't work so she now lives 5 minutes away at a Memory Care Home. After a transition period, she seemed to settle in and be content, but that changed in June after a visit from her brother (who also has Alzheimer's). She became agitated and angry, and we suspected some type of physiological change in her condition. So she had cognitive tests, an MRI, and then today a follow up with the neurologist.

At the same time, all the upset and rage has diminished, and Mom is once again fairly content with her life. She goes to the gym twice a week w/personal trainer, plays cribbage once a week, gets books from the Library weekly etc.

The official diagnosis is Alzheimer's as primary and mixed Dementia due to vascular damage focused in the temporal and parietal lobes. Her MRI slides showed lots of black, which is apparently dead/damaged space in the brain. So the doc said Mom was in a moderate-plus stage.
The doc also said, Mom's medicines were good and the only change she recommended was for mom to stop drinking Diet Coke or soda of any kind.

This will improve Mom's mood (which at the moment is good)

That's it.

So we have an official diagnosis, and I have no idea what that really means.