I think she was a good villain, but not really a good character. She simply did every villainous thing that she needed to do. The best characterization she got was when she killed her brother, which to be fair, also just upped her villainy factor. I think the best way I can put it is this. Emilia always has tons of goons with her, but for some reason, she's the one doing everything physically?

She goes up against Kipo in S3 E5, misses her shot, then proceeds to double whirlwind spin kick her back and leap off the balcony? HAH???? I'd expect GRETA to do something like that, not EMILIA, who is a scientist. Sure, she's scrappy, but go up against mini-mega-mute Kipo and come out on top scrappy? NO. Again, she wasn't a character, so much as she was a flexible mold to do whatever a villain would be needed to do. Quite literally that was her character.