It really just sounds like someone trying to figure things because that's confusing.

I get preferring they/them, but I don't understand being okay with a gendered pronoun like "she" but also being heavily offended by "her"

I have no problem with using people's preferred pronouns, but this seems so niche that if someone truly got angry at me over this, I probably just wouldn't associate with them.

A person with such a specific preference has to understand that most people are going to have confusion regarding this.

People with bad intentions aren't mistakenly saying "her" instead of "them"; they're the types of people that would say "him", intentionally misgendering the person.

I think patience towards those trying to get it right is important.

My dad is right-wing and older, but he's fine with using preferred pronouns, but his main worry is making a mistake and being yelled at for it (He has social anxiety issues)