I’m sorry none of that has anything to do with ADHD. If anything ADHD is great for helping make connections from disparate sources as, for better or for worse, 15 things pass through your brain every second. And as someone with ADHD, trying to talk to me during a movie is incredibly annoying, because I’m either hyperfocused on the movie or working very hard to focus on it. If I’m not focused on it, I probably don’t care about it very much, so I’m not going to be asking questions to try to keep up.
All of this sounds like your sister has made “ask questions” part of her “try very hard to focus” routine but that is her quirk, not an ADHD trait. I can only imagine nobody has annoyed her in this way so hasn’t thought about it.