My MIL (83yo) does not realize her pull-ups are soaking wet and refuses to change. What can I do?

With dementia, they truly do not understand the basic facts of nearly ANYTHING. I tried telling my mother that even though her electric toothbrush wasn't running, it could still be used as a toothbrush. I told her about 10x and still, no comprehension whatsoever. She insisted I throw the toothbrush out because it no longer worked. Sigh.

Your MIL has no comprehension of a wet pull up, and no concern for the fact of the matter, either. Dementia kills off their sense of smell as well, so to her, there is no odor to bother her. Your best bet is to read all you can about the disease so you will be prepared for what you will be dealing with. Here is a link to an excellent chart of the 7 stages of dementia & what to expect during each:

https://www.dementiacarecentral.com/aboutdementia/facts/stages/

Grandma's idea of a toileting schedule is your best bet.

Wishing you all the best of luck dealing with the issues that these 2 diseases bring along with them :(

You need to set a bathroom routine.
Every 2 hours wet or not bring her to the bathroom and have her try to go. This will give you a chance to check the brief and change it if necessary and change clothes if needed.
This is a don't ask her if she has to go..this is part of her routine. Every 2 hours is bathroom time. You could make a snack as part of the routine, bathroom, wash hands, go to the table or a favorite chair and have a snack.
You can not convince her that she is wet and needs to be changed her mind can not comprehend it and it is not worth an argument.

Agree with above. I was going to suggest tell her nicely instead of asking, be a bit more assertive like, time to change your pullup. Theraputic lies can come in handy. The doctor says you have to change it now (or every 3 hours). It's not wet? Oh, that's OK, we still need to change it. Here we go, lift your left foot, etc.

Oh the joys!

Is she capable of changing them on her own or does someone assist her? One of the things I learned early on with my mother, who also had vascular dementia, was never to ask her to do something. She always said NO! In the case of taking a shower, which she would refuse if I asked her if she wanted one, I would just say calmly, "come with me" and I'd lead her to the bathroom and get her in the shower. She would then do it without refusing. Can you just ask her to come with you and then lead her to bathroom without mentioning the wet pull-ups?