I would cut down on the threats if I were you. All it tells her is that you are afraid that she won't comply- so you're handing her weapons. Also, incidentally, you're probably frightening her; children find it scary if their parents are afraid of losing control.
Your default position must be that you are in control. That you are the grown-up, the person with the experience, the credit card etc. So you don't need to prove that. Just tell her calmly that it's bedtime, and if she won't comply lead her calmly upstairs (if at all physically possible). If she won't eat, don't say dramatically 'your dinner will go in the bin', just ignore her- and her dinner will go in the bin. If she is obviously silly- like controlling what others eat- can't you all just laugh at her?
My advice would also be, never move goalposts. If you have said 'no treat unless you do X', then you can't withdraw the treat if she does X but does it in a manner you don't like (defiantly, laughingly etc). Otherwise it just becomes a power struggle, where she thinks you're just giving her orders to check if you're in control.
I would not have punishments that take over a week before they come into effect, anyway (like no party next week if you misbehave tonight). This means a week of the two of you being on bad terms, which means she can think up further naughtiness which you then have to punish...it can go on forever. Not good for family harmony. Any punishment should happen quickly. I think confiscating something and keeping it away for a week is ok, then the initial anger happens straightaway and they will hopefully have forgiven you by the next day.
In our house we have a rule that we won't let the sun go down on our anger. In other words, however badly somebody has behaved and however furious we have been, by the next morning we start again. (This goes for me and dh as well). The idea of starting a new day by reminding dd that she's potentially naughty seems dangerous to me. Once she's started thinking of herself as somebody who's more likely to be bad than good, then her motivation for being good won't be very strong.
I know we rant a lot on MN and that's fine, but when you seem to suggest you haven't seen anything positive about your dd for a week that seems terribly sad. Are you sure you've been looking properly? I would start emphasising the good things about her very strongly if I were you.
Finally, it seems very important that you and your dh do not undermine each other. When you say, you waited to see how dh would handle it before you set in- does that mean you're not deciding together on matters of discipline? I think you need to sit down to a long talk where you both listen to each other.