I wouldn't assume anything. And it might not be related to sensitivity in general, but sensitivity to a particular chemical. (Also, is the perception of smell tied only to sensory aparatus in the nose?)

> finding others with it is a bit of a chicken-and-egg problem: how do you efficiently screen for this without knowing the precise compounds are to be targeted?

Expose them to people with Parkinson's; based on her experience, it seems like a quick test. In her case, they tested it with t-shirts worn by people with Parkinson's.