Lots of interesting replies here.
It’s very much like @nakedavengeragain’s post. Talking to herself about what she’s watching on TV, narrating what other people must be thinking and doing, speaking her thoughts out loud (even if they’re rude!). It definitely isn’t rehearsing or practising upcoming conversations.
She doesn’t live on her own so she does have company at home.
I think she has a number of ‘quirks.’ Without any consultation from others, she plans and scripts how upcoming events will go, and then when they don’t go according to her plan, she gets very upset. But of course, the people around her don’t perform according to her script or plan (why would they? They don’t even know it exists!) but then they get told off for not doing what she had presumed they would do!
She never asks me any questions about myself. She monologues. She talks to me like I’m a little girl (“you’re doing this wrong, that’s not how you’re supposed to do that!”). If I am telling her a story because I’ve managed to get a word in edgeways she cuts over me, finishes sentences for me and gets visibly irritated if I ‘go on too long.’
I do wonder if it’s some broader misunderstanding of pragmatics, context, not quite grasping conversation cues and social communication. I guess I’ll never really know, but last night it really did make me wonder!