If you claimed that you cannot trust her, because of this standard she has of judging which actions to take, she would quite sensibly correct you: you can trust her to act in the way she perceives to be in her own best interest. Or if she has slipped by accident into thinking that a human-independent scale of behavior justification does exist, you can trust her to follow that illusion as long as she is under the illusion; whether you notice this slip and choose to take advantage of her or not, is your affair. She would of course prefer you didn’t take advantage of her; and to protect herself and to ensure that social force is brought to bear against you if you try to take advantage of her, she will choose to put her defense in whatever terms of ethics the power-group she wishes to manipulate is currently using.
Interestingly, for her self-gratification to be maximized, it is to her advantage (whether she realizes it or not) for most people to remain confused (as she sees it) about the reality of what ethical behaviors actually are; because if everyone behaved as she did, then they would pay no attention to any appeals she makes in the language of ethics!
So in such a world: if it offended her for her child to be required by a school to participate in a pledge of allegiance that included “in God we trust”, then she could tell them she was offended, and they would probably recognize it as a fact, but the child would still have to obey the rules and participate in some fashion, or suffer the consequences. If she threatened to sue them, in order to bring social force against them, she would have no grounds upon which to base her claim except the raw fact that she does not want her child to (effectively) learn to pray to Someone she doesn’t think exists. There would be no laws about this to appeal to (in such a hypothetical world); there is no reason why a majority should make exceptions for an individual’s self-gratification, unless the individual has the power to draft (and ensure enforcement of) the laws, in which case appealing to the law would be a waste of time anyway–it would be better to merely apply the effective power directly to the problem! (If this description sounds like any number of supposedly ‘democratic’ tyrants in our world’s history, it is hardly by coincidence…)
Still, ‘invented ethics’ can (at least in theory, and even in practice in some ways) be a self-consistent claim. True, the proponent of the theory won’t come out and explain exactly what she is doing when she appeals to fairness or rights, while she is making the appeal; but that is only because she knows nothing would get accomplished if she explained what she was really doing. The duplicity involved does not mean her theory is false.
Let me also remind you that this notion is not restricted merely to secular humanists and/or other atheists/agnostics. It can also be applied by people who believe God exists and is amoral. And there are other ways to accept this theory, too, as I will show later.