Off the top of my head they sound like they are .... uhm.... what's a nice way to put this on the internet. OCD Autistic?
In short, the type of person this sounds like that I've worked with before, will not understand why you haven't changed it until you tell them point blank "that is the ending, and it will not be changed." They can gripe and be upset, but they need to be told very clearly that the ending is what it was.
Take a kid to the movies and they wonder why the Titanic sunk. You tell them that it was history, and it really sank - That is the end of the story. It will not change.
The best you can do is tell the person that it will not change just because she wants it to be different. But... don't word it like that. Honestly word it more like I did before: "that is the ending. that is the story. that is how it was made and released. no one can change it." Make it as solid as a rock without bringing her/their emotions or views into it. Otherwise it sounds like an attack (to this specific type of person).
I may be wrong and they may not be the Austistic sort, but I've worked with several to know that sometimes they bear being told a few times. Just make it a broken recond response. "That is the ending." Firm. Solid.