I wonder if he thinks maybe he's doing her a favor? Maybe he figures she'll enjoy the holidays more if she thinks she doesn't actually have Alzheimer's?

When my mom was first diagnosed with dementia, it was very hard on her, because so many changes happened at once. She was losing control and it was frustrating to her when she'd forget, especially if people reminded her she was forgetting something.

Maybe you can just go along with this through the holidays (assuming you celebrate the season) and keep an eye on her, and take her back to the doctor in January if things seem to be getting worse.

Try not to worry too much.