Our daughter thinks she has an equal say in any of our decisions. She only does the things we tell her to do if she thinks they make sense, otherwise we have to threaten her, which makes her threaten us right back. Most of the time this isn't a problem -- she takes arguments about going to bed, brushing her teeth, eating vegetables, doing homework, practicing the guitar the way we want her to, but the other day she was going to take a bucket of water and clean some shelves downstairs and I told her NO and she said Why not and I said I didn't want her to. She picked up the bucket and said that isn't a reason and started to walk out of the bathroom. I told her I would punish her if she continued and she said SHE would punish ME if I did. She means it, too. As you probably guessed, yelling doesn't work, she yells right back, and we don't beleive in smacking kids. She finally stopped when I promised her I would let her clean those shelves with me over the weekend, but how to I get her to do what I want her to do because I said so? Her dad isn't home much but she's not much better with him, except if he yells really loud, which isn't dignified, and that doesn't always work either.
When I say threaten her, I mean I say "If you take that bucket out of the bathroom I will take away your DS", and she says "If you do that I'll hide your credit card". Anything we think we have a right to do to her she thinks she has a right to do to us.