I reject her analysis that we are witnessing “narcissistic populism.”

No, what we are witnessing is populism, period. Yes, its present American leader happens to be a narcissist, but that does not render the movement "narcissistic populism.”

I mean, what is that phrase even trying to mean? Is it trying to pretend that narcissism (vanity, craving admiration, egotistical self-love) is somehow more a feature of populism than it is of, say, traditional conservatism or of leftist activism or of liberalism or of Marxism?  

I do not see populism to be particularly narcissistic. Indeed, narcissistic" would seem a far better fit for activist movements such as Black Lives Matter, Toronto Chapter, which is pretty far away on the spectrum from the bunch in question (US populists).