There's this running sentiment that I've seen a few times recently that, in absence of being recruited and subsequently abused by Trent, Astrid would have been someone nice (read: "good") and in touch with her emotions, or something, instead of pursuing power and authority. It's an idea that seems to purport that Trent fully brainwashed her into being a completely different person acting entirely against her own volition, because surely if she was somehow fully cognizant of her "real" wants / feelings / had friends, she would simply walk away.
Except that she wouldn't, because she didn't.
We are told repeatedly by Caleb and reinforced by Astrid herself, that she is and always has been ambitious. If freedom from Trent was all that she was truly after, then she could have had an easy out once the Nein removed him from power. But instead she stays to take her place in the Assembly, because that was her goal all along.
In fact, Astrid's ambition would have made her more susceptible to Trent's manipulation, especially when she was younger. The way that Astrid and Eadwulf murder their parents is very personal and intimate - strangulation and poison at the dinner table. Neither of them flinch, and yet Bren's method is to not even show himself, but barricade his family in their home from the outside and then set it aflame. It was a comparatively anonymous act, but he was the one to break.
Trent's miscalculation here of course revolves around Bren's character. We can probably attribute him overlooking this because of Bren's clear aptitude, and then perhaps following the assumption (which has tbh proven time and time again throughout history) that a wizard capable of achieving great power will always go after it no matter the cost. Although Liam says that if Caleb had met Astrid and Eadwulf again much earlier in the campaign prior to forming strong bonds with the Nein, he likely would have gone back with them (juicy juicy AU fic of where this happens exist out there I'm certain, but also further illustrates that Caleb himself wasn't fully immune, obviously), part of the reason why Caleb's arc is so beautiful is precisely because of his journey to stand in contrast to this cliche.
It is further interesting, then, that when Caleb does come back into proximity of both Astrid and Trent, with no small amount of ability, that Trent still immediately fixates on him, even though he is better able to resist Trent's manipulations than ever before. Astrid has been at Trent's side for well over a decade at this point and is obviously a very capable wizard herself, seemingly loyal - even if Trent probably had doubts about the true depth of her loyalty to him, then at the very least loyal to the Empire - intelligent, and politically savvy; all things you would think would still make her a prime candidate for successor.
It begs the question of what Trent found wanting in her, that he would decide to so blatantly favor Caleb, someone he arguably cannot actually control, over someone he has personally cultivated for years.
It's obvious that during the dinner, Trent is working many scummy manipulations on Caleb. But by proclaiming "nothing would make me happier" to have Caleb kill him and take over, he is simultaneously twisting a knife at Astrid, firmly shunting her into second place, if such a place exists at all, as far as he's concerned. We can probably assume that Astrid's ambition to actually do precisely that aren't entirely a secret from Trent (frankly he'd be very foolish to not expect it of people he manipulated into murdering their parents as children), and he would also be very aware that he still outclasses her in terms of raw power. Astrid, or even Astrid and Eadwulf together, aren't strong enough to take him out on their own, so it behooves Trent to prevent any possible alliances from forming by trying to drive a wedge between her and Caleb. The goal of this might not even necessarily be to prevent his own demise, but set up a familiar "test": if one takes out the other, then he'll know who is really worthy of being his successor.
Of course this isn't what happens, because Caleb's reappearance in her life has already begun a shift in Astrid. When we first see her "on screen" in episode 89, it's pretty clear she's got a front up and is touting the party line / is in the sauce, so to speak, and as "genuinely mournful" as she is, she still seems to firmly believe that the suffering they endured was for a reason. Even so, she heavily hints to Caleb that she isn't so unfailingly loyal to Trent that she wouldn't try to usurp him.
There's definitely something a little 'off' about the whole interaction - on a meta level, this might be largely because she's a brand new character to Matt that he's still getting a feel for, and on a narrative one, someone she once loved very much and has been either catatonic or missing for a decade suddenly showed up at her house - but something has definitely shifted by the time we see her again, and in other scenes in subsequent episodes. Ultimately, she's very clearly conflicted about the position she's in: Caleb and the Nein can be the convenient means to an end that she wants, but it could also mean sacrificing him - because if they can't defeat Trent, it's not worth risking her own life to stand with them. It's clear that she still carries many deep feelings for Caleb, and as much as she doesn't want him to die (perhaps especially not by Trent's hand), she's not quite willing to die herself.
This is why she helps Caleb get the medallions, why she (allegedly) cries in the alley, why she and Eadwulf warn Caleb ("we're not doing it for you, we're doing it for him") about Trent coming after them, why she lets him complete the scroll in Yussa's tower. She needs Caleb to help take Trent out, but it has to happen at the most optimal moment, otherwise there's no point - this is why she doesn't help the Nein in the final fight until it's clear they have a chance of winning it.
There's a lot we don't know about where Astrid's true hatred and resentment of Trent stems. Certainly the myriad abuses all three of them suffered, and the unknown extent of that which followed when it was just her and Eadwulf left, but apparently it's been "years" that she's dreamed of ultimately killing him. The amount of rage and anger in her when she is prevented from actually doing it is frankly one of the most profound moments in all of C2. She has the person who has caused her and the two people she probably cares for most in the world immeasurable pain and trauma finally subdued and at their collective mercy, and yet is told "no, you can't kill him, we want him to go to trial"...by one of those people.
It's a betrayal, in a way, and perhaps more than any other moment, clearly demarcates the differences and fractures that exist between her and Caleb as they currently are. Astrid further underscores it by specifically putting Eadwulf away from Caleb (and Eadwulf looking back is one of the tiniest but such important little glimpse we get into his feelings) and simply leaving.
It's a terribly bitter moment; she's more or less gotten almost everything she's wanted for a very long time, but gets to derive no real satisfaction from it. She walks away, furious, resentful. But after a time, they do come back - and my personal theory is that Eadwulf convinced her to do so. Obviously they see enough value in Caleb and Beau's plan to spend the exhausting hours recounting their experiences, as perhaps if this is the only way to allegedly ensure that Trent gets locked up for good and getting any kind of justice (revenge), they don't necessarily have much to lose if they're careful not to jeopardize their political positions with the rest of the Assembly.
And of course, naturally, still, Ludinus offers the job to Caleb first.
(Obviously there are narrative and meta reasons for this, but it wouldn't be a stretch to imagine that it wouldn't have further twisted the bitter knife in Astrid just a little bit yet).
All of this is to illustrate that yes, Astrid and Eadwulf did suffer abuse under Trent, but it's a mistake to use that as the sole explanation for their actions and motivations as fictional characters, or to use it as a way to give them an avenue to being "good" people underneath it all - ie, removing the teeth from their roles as antagonists.
Which is to say: people often have an especially hard time when characters exist in a shifting grey area of morality - especially women. Astrid (and Eadwulf) has always occupied this space within the narrative because of her dual proximity to Caleb ("good") and Trent ("bad"), but it would be a mistake to believe that her character arc is simply her choosing between the two of them and what they allegedly represent. At no point does Astrid ever explicitly agree with Caleb about stopping the Volstrucker program as it exists, and we've never gotten any clue in the subsequent story years later whether or not she actually did anything directly to dismantle it. We can infer that in absence of Trent it might have ceased perhaps at least in part, yet for as important as that is for Caleb, and even as much anger and rage Astrid obviously has towards Trent, she has been pretty much reticent on the subject in canon material so far, to the point that it seems unlikely it's a primary motivation for her to take over Trent's seat. Perhaps after several years of close proximity to Caleb (because Liam has not mentioned her multiple times post C2 proper for them to not be talking on the regular), she did do something about it, but exactly what and how much is all speculation.
(Sidebar: further to the last parenthesis above, Caleb was absolutely the one to hide Astrid in Chastity's Nook during the events of C3, and Essek saying "Bren sends his regards" was in fact a signal to her that he is an ally, and if he said it like a threat, it's because he's a catty bitch (affectionate), which further plays out in their subsequent interaction).
As I (and many other people) have said in the past, we shouldn't be afraid to let villainous / antagonist characters be bad ("problematic"), and we shouldn't be afraid to enjoy them because of the role they occupy in a story. Astrid is compelling precisely because you (the audience, the Nein) didn't know which way she was going to go in those pivotal moments, whether she is friend or foe; she's compelling because she doesn't immediately fall in line with Caleb's plan to imprison rather than kill Trent. All of those layers of tension and conflict are what make the story juicy and interesting. Trent is a motherfucker and makes my skin crawl, but he is a fantastic villain. Astrid doesn't "need" to have a full redemption arc for any reason, and especially not to justify her continued proximity to Caleb.
I always feel it's very remiss of discussions that involve Astrid and Caleb to not include Eadwulf - I've mentioned him several times by proximity, but not so much about his position in all of this specifically, which is an unfortunate symptom of the fact that we simply don't get a lot of exposure to him by comparison, and he's never the focus of the scenes that he's in. It is my hope that the animated series will be able to correct for some of this and build him out a little more, much in the way we got to see him in Caleb's origin comic. The two moments there that always stick out in my memory are him and Bren being the first ones to initiate physical intimacy, and him striking Bren and leaving him to stop him from attacking Astrid - it's such an incredible parallel with the moment that Astrid pulls him away and he looks back at Caleb. There are so many other little hints, like his raven feather necklace, the way he speaks in front of Trent at the dinner (being a dutiful soldier), his encouragement of Fjord, that seed all of these little nuances that are lovely on their own, but still leave me hungry for a fuller picture. In my mind, he's a necessary anchor between Astrid and Bren, and eventually singularly for Astrid, who probably needs him more than he does her, in some ways. I like to think they love each other more than anyone else in the world, but to speculate further is getting deep into headcanon territory (not inherently bad, just not the point of this post). Of the people who would "just leave", Eadwulf by his own admission said he'd be fine with that - so perhaps he did stay solely for Astrid, and maybe once Trent was ousted, he did leave, for a time. But it's likely he would have found his way back.
Anyway: love a problematic fictional woman.