there is a difference between ruining an entire game and ruining my enjoyment of a game.
You literally said "it ruins the rest of the story." Not "it ruins my ability to enjoy the game."
I also find it interesting that me insisting that the feature does not work in this case is important to me essentially got ridiculed by you (“Well, I'm sorry your ability to enjoy a game is so easily ruined.”) while at the same time the exact opposite is perfectly fine with you (“Of course, it may ruin that player's ability to enjoy the rest of their story”) if they cannot make use of their feature this once.
I'm just pointing out the hypocrisy. You're not playing a solo game here. You're playing a group game. Sometimes you have to give a little, especially on matters that are not disruptive or harmful. Why is it better that
their experience of the game potentially be ruined--and along with it, potentially their trust in the DM's willingness to be fair with them? Why not just
ignore it the probably one or two times in an entire campaign that it may come up?
I mean, are you seriously saying that if a player used this ability in a way you find improbable--but that helped move the plot or her or someone else's personal goals along (or at least didn't hinder them) and wasn't harmful to anyone at the table--that you'd still be miserable about it sessions later?
At my table, we have a player who loves giving her characters exceedingly silly names, particularly when she plays members of certain species. I
hate these names, because I'm trying to be immersed in a serious game and use serious naming conventions. Do I make a big deal about it? Do I tell her (when I'm the DM) she can't use that name or demand the DM (when I'm a player) make her change the name?
No, of course not. Because it's a group game. She's a good player and a lovely person. She works well
with the group both in and out of character. Her silly naming conventions aren't actually ruining the game or my enjoyment of the game. I get really
annoyed when I have to use her characters' full names, but annoyed =/= ruined.