Retaliation, yes, but if the passenger believed she smelled alcohol on the captain (and several other pax also seemed to smell the same thing), you would think she would have voluntarily deboarded herself.

That's what I'd do. If I truly believed I had smelled booze on one of the pilots, I wouldn't believe whatever story the good-ol-boy network of pilots/FAs/GAs/etc said about him "passing" a test, and I would get off the plane. There's just no way to tell who might be covering for him, and I would believe my own senses over a claim by some stranger.