Hi clueless and welcome to TP.
I have to say that I'm pretty clueless too but if I bump your post a bit somebody will come along whow can answer your question much better than me.
First off, there are different kinds of dementia. Alzheimer's is the most common closely followed by vascular dementia and there are lots of other dementias as well. My MIL has vascular dementia so I don't know all that much about alzheimer's but I think this thread might help you.
Stages of dementia
I did look at the stages of dementia when MIL was first diagnosed and found she wobbled about between stage 2 and stage 5 so I sort of gave up and relied on TPers to help me understand what is going on.
It sounds like your Mum is doing really well, my MIL is 86 and, sadly, in a care home now as we just couldn't meet her physical needs at home.