It is odd that you failed to quote her but instead put a video up. Her exact quote was:
“If public health professionals, if Dr. Fauci, if the doctors tell us that we should take it, I’ll be the first in line to take it, absolutely,” she said. “But if Donald Trump tells us that we should take it, I’m not taking it.”
She then went on to take it. I guess Trump failed to tell Harris to take it, I guess. Heh.
It's all pretty easy to explain. Democrats didn't trust Trump and were more likely to be hesitant to believe anything he would say because Trump isn't a doctor nor an expert and in matters concerning Covid, despite all the experts around him, he's been more often wrong than right.
It still doesn't explain why most people with vaccine hesitancy are from areas where Trump did well in votes.
https://www.coloradohealthinstitute.org/blog/data-show-politics-has-become-powerful-driver-vaccine-hesitancy
https://www.nytimes.com/interactive/2021/04/17/us/vaccine-hesitancy-politics.html
https://www.npr.org/2021/03/19/978407316/how-do-you-reach-trump-voters-who-say-they-dont-want-the-vaccine-try-doctors
Even Trump and his allies have urged his supporters to get vaccinated and yet the hesitancy persists:
https://www.usnews.com/news/national-news/articles/2021-03-17/trump-tells-followers-to-get-vaccinated-against-coronavirus
https://thehill.com/changing-america/well-being/prevention-cures/549151-trump-tells-his-followers-to-get-vaccinated
https://www.forbes.com/sites/brucelee/2021/07/26/sarah-huckabee-sanders-calls-covid-19-vaccine-the-trump-vaccine-urges-people-to-get-it/?sh=67d1b55325a3
So, it seems even stranger that Trump Supporters don't trust Trump now that he is no longer in office.
Now, I'm sure you'll be happy to impugn any of these sources, but take notice that I didn't have to impugn yours to make my point. Why don't you try to do that in your reply?