I'm sorry but I don't see the point Red Queen is making.
It seems like you're worrying about how other people will play it out, and them 'having it all'.
No, I don’t think that’s what I’m doing. I’m saying that I want to be able to *try* to trick Ethel for her hair and then kill her, but fail. I find that a more interesting and impactful story than one in which I can straightforwardly kill her after deceiving/intimidating her, or just let her go without trying to stop her. My instincts are that it shouldn’t be possible to get both the ability point and kill Ethel, both as I think it’s a bit of a cop out dramatically and in light of Ethel’s other deals breaking when she dies.
But it is a fair enough challenge that the game should allow other players to tell the stories they want to tell, too, and in a D&D game that sounds like something that could be left to the roll of the dice.
I’d see it as a fair compromise if there were some further skill/ability check after you’ve done the deal that could then lead to either you killing Ethel or her escaping. That could be a melee check to catch her, an arcana check on magic she’s using, or a selection of different possible checks like when trying to get out of Astarion’s hold if he catches you when you first meet.
