Because they were real and meaningful to her. Even if her sister manipulated things, and introduced some fun plot elements. How she feels in that moment is very meaningful to her.Okay I don't get why she/he is so hung up on the emotions disappearing when in all likelihood they are just as much a part of the sisters fucked up game as everything else was at the end of the day.
Tbh from past chapters not taking itself too seriously, I can see that coming. Sis is troll-ish but not like actually want to kill those two. Sis could say reasons why she brought those two in particular to the game world is because she knows that (speculations, not spoiler) Taiga had feelings for Azumi but two guys dating, social construct etc etc. and or maybe because she's a fujoshi troll or real world is ending or something.The author made the mistake of making her very very hateable, there's no coming back from that. Not even in a funny "haha, it was all a trick" way. Event the chapter title is telling us that.