Lucelia: "I deserve more magic crystals! I've literally never done anything wrong in my life."
Her sister: "A lot of people hate her and she gouged out my eye."
Lucelia is not saying she deserves more magic crystals than Syl though; she's saying that, since both she and Syl killed the same amount of monsters, they should get "paid" the same amount of crystals. It's still a cheeky thing to say, but hey, she's a gremlin and I find how she's depicted hilarious.
Also, I don't think Lucelia remembers any of the things with her siblins since it was done under the influence of the demon king's claw stuck in her skull.
As far as we know, she used to be bullied by her siblings for not being as ruthless as other demons (and also her ancestry since some other woman considered Lucelia's mother to be lowly) and only flipped the script on them after the demon king stabbed her in the eye.
I've got no clue what the demon king was thinking though. I mean, first he stabs her with a piece of him, influencing her mind to be more evil and also granting her energy (or at least some way to ignore the servant summoning limitations), and then she's punished by getting dropped into Bersoil the demon killer - which couldn't actually kill her thanks to the extra energy from the demon king's claw but instead just restrained her. And that's the thing, the demon king's energy was also getting sucked by Bersoil, so he was making himself weaker through this. There basically was no possibility for any other demon to come and free her since Bersoil would capture and kill them, so really only the demon king could potentially go there and free her?