Probably not ever going to be officially diagnosed

The changes you describe are strongly suggestive of some form of dementia, and/or mental illness. Highly educated professional people can be difficult to diagnose because they are able to compensate for some cognitive losses better than the average person, or to just cover the impairment up. It would be helpful to notify her doctor privately of your concerns, with specific examples of changes, that might allow him to order some targeted screening tests such as blood and urine tests and perhaps an MRI. She might or might not accept his recommendation of neuropshychological testing, which could provide much more information. Are you observing significant short term memory lapses, changes in her language function, repeating herself? Has she gotten lost while driving or had minor accidents? Is she able to manage finances (keep up with bank balances, pay bills on time)? Or is her husband managing all the finances? Does she do grocery shopping and make appropriate purches? Is she able to follow a recipe or cook a meal? Some patients with dementia are aware of their cognitive loss and fret about it. Others are either unaware or are in total denial, despite the evidence. Without a definitive diagnosis it is difficult (impossible) to make decisions. It cerainly would be beneficial to have general power of attorney, wills, living wills and healthcare powers of attorney in place for her and your dad if at all possible. It is a nightmare to have to go through courts to get things done. Good luck.

@wctdoc1943 thank you for this post. Sorry I disappeared from the community for a bit. Everything that you wrote resonates with me. Let me respond to your questions:
Are you observing significant short term memory lapses, changes in her language function, repeating herself? YES - absolutely. This seems to be dynamic. Every day is different and sometimes it changes throughout the day.

Has she gotten lost while driving or had minor accidents? Most likely because there are long time lapses between when she leaves and returns and most often she says she is going to one place that is nearby. Fortunately, she is not driving much these days. I believe she is aware that something is not quite right and this is why she will stay home all the time. Plus and minuses there.

Is she able to manage finances (keep up with bank balances, pay bills on time)? Maybe. She's old school - so she still writes check for a couple of bills and mails them at the post office. My father has always managed the finances. Before dementia - she was not good with money management. I have noticed a pattern of anxiety with anything financial - anything with numbers (review anything or even conversations related to finances).

Does she do grocery shopping and make appropriate purchases? Dad does all the grocery shopping. She has always loved to shop. This has always been a coping mechanism for her. It is a problem now with dementia because she is aware (I think) of her illness and her shortcomings now and will shop as an escape. This is my own thinking here though and a pattern that I am recognizing.

Is she able to follow a recipe or cook a meal? A recipe- probably not. She will make what she remembers to make - which often is the same thing over and over again. The meal will be simple and not sufficient though - we help to supplement. For example, she'll just make a salad or just make a protein. She is not really able to consistently create balanced meals. She'll just grab things to heat up that are not appropriate for breakfast, for example. But this is not all the time. On a really good day - she pulls together a great meal independently - but then she is completely wiped out after that. She has a fixation with chopping (honestly scares me a bit because unlike many folks have shared on here - she is NOT sleeping)- although it's not as bad as it was say a year ago. Last year, she would chop everything at once - onions, carrots, peppers, tomatoes (some of which you'd chop as needed). We'd realize everything was chopped and we'd have to rush to use/eat things quickly. Now it is just carrots thankfully. 🙂

I love that you offered "Some patients with dementia are aware of their cognitive loss and fret about it. Others are either unaware or are in total denial, despite the evidence." I think she is a mix of all of these. Again, it depends on the day but overall - she's typically angry and combative which is very difficult for me and dad because we cannot get a solid plan for how to support her more routinely. Most often, she'll blow up at us over things we try to help with (because help is required, for example, with her dog) and when we try to talk about things together - she'll leave the room, go outside away from us, or previously leave in her car (this is not occurring now thankfully).

Don’t know if this approach might help or not, but I would give it a try. Instead of talking to your mother about her mental status, her changes, her decline, etc. drop that topic altogether instead bring up solutions without ever mentioning her problem. Something like, wondering if we Get a housekeeper to help me keep everything tidy. My friend Jane is very lonely and wants to develop more friends in the area so I wonder if it would be a good idea to have her come over and spend some time with us.

I found with my mother that discussing anything of that nature was never very productive however, she was always a pretty sociable, woman, and when helpers and caregivers came to her, she eventually saw as a visit from friends not as caregivers! I would give it a try. I think with a lot of people whether they have memory issues or not as they get older Their instantaneous response to any outright conclusion/statement is a great big no! When it’s presented in a friendly or non-caretaker way, I. E. A friend coming over, you may still get an initial note that won’t be quite as strong, but as you will be present in the early stages, you can just approach it that she’s here for me! Then you gradually work yourself out of that equation. Not sure it would work all of the time, but I do think it might work some of the time?