oh right, i talk about the past when rosie did something horrible to eve (did we get the explanation?) bcs sometimes it's hard for me to think that she is have an innocent side when we know what happened in the future if eve didn't changes.
but anyway now we haven't been there yet sooo where's should i put rosie?
I’d put Rosie as a victim of circumstances. The only thing she did on her own in the past was give Eve poison. It was the ML who used her as the test subject for a homuncules and human child because she just happened to choose him and make him her knight back then through the philosophers stone. The story’s been cementing how even though she’s pretty young and isn’t involved directly in politics, she has the second most real world knowledge behind Eve. She was protecting the position she had at the time, which without Eve to block all of the other siblings from their eldest sister would’ve been an issue Rosie had to deal with
Tldr: Rosie is good and on Eve’s side this time because Eve treats her like a person with her own agency. She wants to be good and Eve is giving her that chance while gaining an ally in the social scene

i think i marinate this one too long, just see a few page on the last chap. actually i'm quite shocked, so rosie get redemption or something? can someone spoiler that for me?
and i'm just saying, it's so stupid for not change the color of the hair like rosie did.. what the purpose of the mask if everyone still knowing it's you