I mean, Remilia isn't being redeemed for shit. She ultimately remains a sociopath through and through, and even her one act of sincere pity/empathy is still laced with '...and Emi likes you so hey why not.' All Remilia is doing is directing her sociopathy at one specific target, so everyone else benefits incidentally. Remilia is a bad person that does good things for selfish reasons. If she were to ever lose the morality chain that is Emi or otherwise believe that Emi wouldn't mind her doing something absolutely horrid, she'd do it without hesitation or regret as long as it benefitted her.
While I do agree with your logic, there is something that I believe you've misunderstood, or forgotten. Remilia was originally from a home that never gave her, or rather understood, the love she wanted ever since she was a little girl, which I believe is why she became so twisted, to begin with. When Emi first possessed Remilia, she was even trying to demand that Emi returns her body to her since it was suddenly taken from her, even though she couldn't be heard by Emi. But, after going through Emi's memories and watching how she did her best in Remilia's place, she has, in essence, understood how she wanted to be and used Emi as her role model.
Now, about Remilia's target for her sociopathic tendencies. While Pina is her primary target, she isn't the only target. She even stated that at the beginning of the series. Pina, the prince, and his posse, those who falsely testified against her, her father, and all of the background characters who allowed Emi to be condemned at that party are her revenge targets. However, since Remilia is using the knowledge from the game that Emi played, most of her actions will be affecting Pina, the prince, and the three stooges.
And I know that what will come up next will be affecting just about everyone else that she has a vendetta against as well as her primary revenge targets.
