The books make it clear times and again that the a'dam is unescapable.
and yet, just because you can't take it off, it doesn't mean you are completely helpless.
premise: you are a prisoner. you will be tortured, abused and broken into killing your former friends. this is a fate worse than death. therefore, death counts as victory for you. if you die, it's a good outcome; you are not expecting to come out of this alive anyway. whatever damage you can deal to the seanchan before you die, that's just bonus.
premise 2: an experienced channeler could just control your flows, like nynaeve did with moggy. however, the sul'dam are anything but experienced. they do not know they can do that, just like they don't know they can channel. you have that little advantage.
with those premises, let's see a few things you could do to foil the empress
1) the martial artist
You cannot use weapons while wearing an a'dam. egwene was unable to touch the brooch of water after she thought of hitting renna with it. But! Book canon establishes that you can still use your bare hands. when egwene was first collared, she punched her sul'dam, and nothing stopped the punch. sure, she was disabled by the pain afterwards, but she could deliver one good punch in the process.
it's perfectly possible to kill a person with a single well-delivered punch, especially if they are helpless because they are not expecting it. i was thinking a solid blow on the occiput, it's the most frail part of the skull and a strong blow there often results in permanent damage. Sure, if you kill - or even seriously wound - your sul'dam you are going to die of feedback pain, but we established in the premise that's exactly what you wanted. you mercy-killed yourself, you denied the empire a powerful resource, and you managed to bring a hard-to-replace sul'dam with you.
you can also try to kill other damane, they are very valuable resources - and whether they are tortured prisoners or willing soldiers, they are legitimate targets in both cases, if for different reasons. killing a damane should be easy, if you can still throw punches and you don't get pain feedback. main disadvantage is, for something like that they are likely to cut your hands, which would prevent you from further exploiting this technique and would make your life even more miserable than it already was.
The main disadvantage is that killing someone with a single blow is hard, even if you can deliver a good surprise punch on the occiput, especially if you are a tiny woman.
2) friendly fire
go along with enslavement. don't resist. play pretend. if the sul'dam sense that you are not truly tamed, just say "[name] doesn't want to be punished", which is pretty realistic anyway. try to get them with the guard down. eventually, you'll be used in combat. you are expected to channel letal blows in that case. when you form a deadly wave, instead of throwing, release it at your feet.
the sul'dam can sense what you do, and can stop you. however, especially if you've been fighting normally for a while, they are extremely, extremely unlikely to be expecting something like that. people have limited concentration, and they tend to get distracted if involved in a monotonous routine. you only need your sul'dam to drop her guard for a second.
the disadantage is that it's unreliable. it requires your sul'dam to not be expecting a suicide move, that she'll be too slow to react. and, if you try it first, it's more likely the sul'dam will be attentive; you will have to kill some of your former companions at first. But if it succeeds, you could take upwards to a dozen damane with you, dealing a major blow to the empire.
3) the stoic
Just refuse to do anything. they will punish you; keep refusing. by tuon's accounting, ryma was about to die before she was broken by playing good cop. it means it's possible to just deny your captors, and ryma would most likely have died had she not found tuon.
it requires a ludicrous amount of willpower, though, if even egwene couldn't manage it.
4) the least amount necessary to kill
While it's normally accepted that you can't channel at all while wearing the a'dam, you actually can. during one of her chapters, egwene was doing just that. and she could channel only a tiny tiny trickle of power, and she was getting nauseated, and she could not open the a'dam. but she could still move small objects.
and it doesn't really take all that much strenght to kill a person with a needle through the eye or ear canal. make a needle of air, you may just be able to kill a sul'dam that way. or at least to gouge out her eyes, which would still mark her a casualty for the empire.
it's even possible you could puncture her eyes, then threaten to kill her if she doesn't release you. if she folds to your demands, you may even potentially survive and escape, but better to not get your hopes up. probably they will find you standing before a dead sul'dam. still, even if they mutilate you, they have no way to prevent you from doing the same again, so they will likely have to execute you anyway.
and you may also manage to kill other damane, which are much more valuable resources than sul'dam.
in the end, there are several ways to defeat the a'dam. sure, they all require a very strong willpower, and most are chancy. and they all will see you dead in the end.
but really, you've been captured and collared, what do you have to lose at this point?
