Yeah, she could smell Parkinson's. I believe it. Dogs can smell all sorts of things humans cannot, and it is possible that a human mutation could grant her such a gift (or curse).

My wife and I smell different scents with differing sensitivities, so I can believe it. (I still remember the smell of roaches from when I was a young child.)

https://www.npr.org/sections/health-shots/2020/03/23/8202745...

But then one day, about 10 years into the marriage, when Les was 31, he came home, and strangely, Joy says, he smelled different. "His lovely male musk smell had got this overpowering sort of nasty yeast smell," she says.