> I don't recall whether she genuinely didn't believe it, or whether she felt it was better to lie to the kids to keep them motivated in the present

She stated it as a simple fact and seemed to believe it. There wasn't any indication that she might think it was a fact of what one might call "political convenience". It made the scene just that much chilling to me: https://www.youtube.com/watch?v=MpKUBHz6MB4