Is my MIL faking it?

Thank you all so much. I've never heard of show timing. I will look into it. Peace.

Mother does this. She can be 'herself' for about 15 minutes and as soon as the conversation shifts away from anything she knows ANYTHING about, she becomes this other person--addled and old.

Why it happens is beyond me. Sometimes she is tired, sometimes she truly is not aware of what is happening, or of who you even are.

I'm not involved in her day to day, or even her month to month. When I DO see her, I see a noticeable difference in her ability to remember things and to make decisions. She's almost 90, so it's not a big shock, it's just that she needs to be handled differently now.

It's called show timing. Yes, just like 2 entirely different people.

The ones that they don't want to see the bad and ugly get the very best they can muster, the ones that know the good, bad and ugly tend to get the brunt of things.

So she is pretending with you and the doctors. Very common with dementia in the earlier to middle stages.

I would say she is more herself around her kids and with staff. She is “showtiming” with others.
Its not something she does consciously.
Here are threads from others on the same topic. See the link below.
It is very common.
The trick is to help your husband learn techniques like those taught by Teepa Snow to help manage the dementia outbursts.(look for her on YouTube).
At the doctors office write notes to the doctor of what’s going on. position yourself behind her. When he asks a question where she gives false info, you shake your head.
Try to find her a geriatric primary who won’t be easily fooled.

https://www.agingcare.com/search?term=Showtiming