You will not sway your Karen niece. To her, a fully university-indoctrinated female, you are an ignorant old Boomer, not smart or enlightened or world-wise like her. (You probably don’t even Venmo.)
Only personal pain and loss from her choices will touch her psyche.
IMO, it’d be best to leave her be and keep praying for the scales to fall off her eyes. I’m doing that with my son of that same age.
Leftist Americans are pretty much a cult now, heavily and continuously indoctrinated by pubic school teachers, college professors, MSM, movies and social media. It really comes down to deprogramming them.
Re: cult...yes, I agree...I feel sorry for her very conservative father...her mother, I believe is also part of the problem.