She was not belligerent, overstating it like that makes it seem like you were the one contributing to the issue.
I rarely shut my window shade during cruise unless the sun is blasting in, which is much more of an issue if you're on the left side of the plane on a Westbound flight. UA's approach of leaving it to the pax is the right one. At some point, it's like masking now. People make their own choices, but don't have the right to cause a scene because they disagree with other's choices. Re: following crewmembers instructions is for safety issues, not sleep or watching movies.