This is about my 7 year old daughter, which wow, I can look back through my questions and see we've had many conversations about.
I'm well-practiced in standing firm, not arguing, telling simply and authoritatively, all that. It works well with my boys. But as for my girl, she has always had the strongest will and the fiercest determination to make it very loud and clear when she does not want to do what you are telling her, right down to screaming for an hour at 2 am because she has to go to sleep and we won't take her to the beach just then. Sometimes it's just funny and hard not to smile, but then there's some days (many days) when she gets up seemingly bound to be a bucking bronco at anything and everything, and on such days she is usually in her room by 10 am, having lost all her strikes, and mama is exhausted and cranky. I'm afraid you are going to tell me to just stay the course... I just get so tired of this self-centered determination to have things her way and exactly the way she wants them. Things on her plate just so, sitting on this couch cushion and not that one, doing this thing first and not that, brother committing the crime of looking at her at the dinner table. It's all these little things of her wanting to get her way that I really need a strategy to make this "her" problem, some clear guidelines for both me and her. The boys just need a firm word and they stop. But she takes that firm word as a challenge to dig her heels in and let me know that I may be able to make her obey the word of the law, but her spirit remains fiercely opposed. That's what I'm most concerned about.
On the bright side she is my snuggle girl that doesn't brood about it after the storm has passed, but returns to being cheerful and affectionate until the next time she is required to do something she's not pleased about.