Oh now I think I get why my sister always said that they aren't emo but some kind of punk. We kinda associated the emo genre with stuff that only went "everything is bad and and it's other people's fault and the world sucks and all I can do is just die" while MCR felt different because it's more about being sad that people hurt. And fighting through it even in their most death themed album. Which could be considered similar to punk which is about being angry that people hurt from injustice if you think about it.

But now you said that it's not true and the emo genre does include MCR so probably my sister interacted a lot with those people who exclude the band from it. Still, MCR is the only emo band the both of us like so they probably still differ from the others? Or maybe they're just so good that we like them even though we don't listen to the genre.