Bear in mind that Abby is a war criminal. Her faction, the WLF, is essentially conducting an ethnic cleansing operation against the Seraphites (and we actually see Isaac lead that). Abby is a "top Scar killer" and she openly gloats about torturing many of these people. These aren't actions driven by survival, defense of community (since Seattle has no communities other than WLF), or any real ideal. It's basically a glorified gang war. She and the ex-Fireflies joined the WLF because after doing war crimes with the Fireflies (which that defector in the Ellie-Joel dino flashback revealed they did) she needed to find other uses for her war crime skills.
And again she and the Fireflies were complicit in a plan to murder Ellie sight-unseen for a vague desperate gambit to create a vaccine for which we have her quack father's assurance was a sure thing. No medical doctor in real life would advocate a measure like that to create a vaccine. That's now how medical science works.
The way to do it, and make her sympathetic was to make her father dissent and be killed by Joel anyway because Abby would be killed if he backed away. That would have given some foundation but what we have isn't sufficient to empathize with her hatred of Joel. She was in the room when her Dad admitted to Marlene more or less that he would not have done it had it been Abby not Ellie. So she knew why Joel did what he did. That makes her a person lacking all self-awareness and self-reflection. Again Daud from Dishonored had self-awareness and self-reflection, so that made the game's attempt to generate sympathy and forgivenes for him work in the end. It's not impossible to redeem a character who falls so deep so fast but it's impossible to do so with the qualities Abby has.