There's been a lot of meta about Kane's father possibly being abusive but none, as far as I can tell, about Abby's parents. I wonder if the flinching isn't a response to possible childhood trauma as well?
I’ve read theories that Abby was abused as a child. At one time, I dismissed it as someone’s headcanon without any facts, but then I starting watching scenes again and then I could suddenly see it and then I couldn’t unsee it. The flinching is an obvious tell, but it’s not just that that points to the possibility of growing up in an abusive home.
Personally, I’m hesitant to talk about speculation too often, because I’m highly reliant on data and evidence before assuming something. Childhood is a long way off for these characters and there’s many places a person picks up beliefs and coping mechanisms in their lifetime (parents are obviously a huge influence but not the only one). I’ll give my opinion on Marcus and Abby though.
First, with Marcus, I don’t think there’s any textural evidence that he was physically abused. However, he has signs of emotional abuse and/or neglect (IE possible absent father who never approved of Marcus and as a little boy, he wanted that approval). Marcus has self-depreciation, even disregard for his own life. That’s some deep-seated feelings of unworthiness, from more than just guilt over the culling. I’ve also read the theory that his inadequacy comes from being born in the working class and having to work his way up the ranks. That makes sense in his professional life, but not so much that it should spill into every aspect of his life. His belief is stronger than just his social rank. He also has great ability to understand other people’s suffering while at the same time has an ability to turn that off and compartmentalize (a learned coping mechanism, almost certainly picked up in childhood). I wouldn’t necessarily say he was abused as a child, but realistically? He definitely has lies about himself that originated in childhood. Being that we know nothing about his father, it seems like a good assumption that the beliefs could be from him, directly or indirectly.
Abby is different than Marcus in that she has self-value and confidence in what she does, so she likely grew up in an environment where she was told she could do anything. Even the rules don’t apply to her. However, she has quirks regarding invasion of her physical space, which points to possible physical abuse. I’m hesitant to just look at details like flinching (flinching from loud noises could just as easily be a quirk from the actor), but the bigger picture points to possible abuse as well.
Some of these scenes were clearly written where Abby clearly has boundaries on physical space. For example, in 3.03 Abby immediately noticed the people watching her in Polis - and it made her uncomfortable. She had no reason to mistrust grounders in that moment, which means she is wary of people in general, and it means she is hyperaware of strange looks and of her physical environment.
She has desire for control in space, and she’s always had that. Even in the pilot episode, she shoved off the people trying to guide her to the airlock. There’s other example of her shoving people away from her if she’s being manhandled. She likes her agency (which is “agggg” to Chipped!Abby). In general, the blocking of her scenes between her and others is deliberate. I’m not sure it can be explained in words and it’s likely too subtle to be GIF-ed, but there’s an awareness that Abby seems to have about her space. Even the touches between Abby and Marcus are very restrained (from both of their ends and there’s a lot of reasons for that) but the important thing of note from Abby’s perspective is that Abby only really physically opens up to people she trust. She initiates touch at times, but people who touch her? Clarke, Jackson, Marcus. That’s it.
I think perhaps the biggest sign that points to childhood abuse is the fact that she hit Raven (2.05) - and felt wrecked by it. The slap was almost out of character for Abby, because she is normally kind and gentle. She doesn’t hurt people, even when she is angry, she either quips at them or glares and walks away.
Abby wasn’t even really angry at Raven. Abby was deflecting because she was upset with Clarke, and Raven was refusing to talk. Still, the slap makes the most sense if it was a learned pattern - not one that Abby wanted to repeat but did in a moment of weakness. In that role in the scene, Raven was the defiant child. Abby has that same defiance - torture me and I’m still not talking - it just makes me think that Raven is a child version of Abby herself in that scene. Like Abby was Raven at one time in her life. And yeah, it makes Abby the abusive parent in the reversal (symbolically, not literally, as it’s not a pattern between them). Raven’s lack of reaction most certainly points to that not being the first time a mother figure has slapped her.
Anyway, long explanation and ultimately of course, we know nothing about Abby’s childhood or parents. Still, based on her reactions, there is a likelihood of Abby coming from an abusive home - enough that she is somewhat wary of people getting too close, she doesn’t like being yelled at, and she’s nervous about sudden movement, unexpected touch, etc. For one reason or another, she is definitely tense and proceeds with caution. Somewhere in her life she picked that up and not just from being on the ground.