Depending on her maturity, you should give her some variation of "The universe is a hierarchy of authority, with God at the top. You are subject to me because I am your parent and that is how God designed things, just as I am subject to my employer and others. There will come a day when people are subject to you, but it is not now." If you have a pet, you can tell her the pet is subject to her authority because she is human and the pet is an animal. So she won't be an idiot, explain why the command you are giving is the best option whenever possible, but when she disagrees that you have chosen well, your only defense is "God made me responsible for you." The knowledge that God is in charge will provide her life with meaning and value that she will not find otherwise, and, apart from the spiritual, her question has no real rational answer that leaves you in charge.