Remilia has become the most unselfish character, since she does nothing for herself, but all for "Emi's Remilia".
Rather than unselfish, I would say her character has always been obsessive lol. After all, she isn't doing this out of the goodness of her heart after experiencing Emi's kindness, she WANTS something to come out of her actions (the people loving Emi's Remilia and getting revenge). And mainly cares about 1 person truly.
Her stubbornly living as Emi's Remilia and planning the ultimate revenge is selfish as well because it fulfills her personal interest, which parallels the extent she went for the prince in the "game" but with a better game plan. (Which I honestly love because it shows that her personality as a "villain" maintained continuity with the game that many villainess stories just throw away)
I will agree that her sense of self can no longer be separated from "what Emi would do/want", which shows her obsessive personality