She never gave Google any reason to believe that she had wanted to walk things back or change her mind. That's the nature of delivering an ultimatum by threaten

She never gave Google any reason to believe that she had wanted to walk things back or change her mind. That's the nature of delivering an ultimatum by threatening to resign: you are explicitly offering an immediate end to the negotiation. Don't be surprised if management takes you at your word, they're not mind readers. If she wanted to signal to managers that she might not actually quit over this, then she shouldn't explicitly say that she will quit over this.