Humiliation?
Well when you march out a defeated, helpless victim-girl to her crucifixion, some things are easy to do but no great accomplishment. Some of the options listed in the poll would reflect rather badly on the perpetrators even if they do succeed at humiiating the victim.
That includes all of the options dealing with fouling the victim with excrement and any other act that's 'dirty'. Sure, throwing shit at her is humiiating, but what does that make the person who does the throwing?
A turd-flinging monkey. Not very Imperial and Masterful.
I would go for those options that keep the dignity of the Authority while they showcase how completely dominated the victim is.
You've got to be in complete control!
Of her and yourself.
Flinging turds doesn't make you look like you're in control.
It makes you look demented.
Showing that you are able to force the victim to comply and cooperate with her own execution would be high on the list, especially if she's a former rebel or high status figure. The way to do that is of course to impress on her how much worse things get if she doesn't cooperate.
Getting her to attempt to offer sexual favors to her tormentors
without directly ordering her to do it would be effective.
It's one thing to
order a victim-girl to pleasure you, any thug can do that.
It's another to bring her to the point where she
herself offers that as a last desperate gamble.
So everoyne sees her revealed as a cheap slut, a common whore, offering up her body for your use just so that you maybe nail her in a less painful pose.
(You have made sure she believes such exchanges might work)
And then, to properly humiliate her, you ought to
deny that offer.
That drives home the fact that you consider her sexual value, her feminine appeal and attraction, to have dropped to absolute zero. She has arrived at the lowest station. She is nothing.
Look at her... a beautiful woman who, we now see, has completely lost the power her beauty had given her over men, in all of her previous life.
In truth she may still have a lot of it but you will not acknowledge. That's the self-control part
Instead you get her to acknowledge her own complete worthlessness.
That ought to be plenty humiliating.
And then the cherry on top of it all is forcing her to orgasm against her will while suffering through her torture.
You need to do that without directly touching her (because she's worthless and why would you touch the worthless thing - something might rub off).
So this is a challenge for your whip-wielding talent.
That ought to be the final humiiation.
(This will probably not happen if you cruelly nail her right away, or whip her with a cruel flagrum that tears chunks of flesh out of her. Again - first practice self-control, then you can gain complete victim-control
)