When you said her attendant do you mean Ludwig ? Since Ludwig only become her attendant after the empire is already in a state of disarray because he's sent to a rural place in the original timeline at around this time, what she said is still right since Sion and Rafina doesn't tell her what she's done is wrong when they are in school like that Tiona dress one.
Other than that in her first life most of the noble or person who get close to Mia pretty much only there for her status as the Imperial Princess so they suck up toher or they have the same view (or even worse) as her. Ludwig is the first person who berate her but then everything is already too late at that time so even though she has changed nothing matter anyway since the Mia they knew are the one in rumors and what they presumably knew from school days.
Wait, you don't remember how Ludwig kept "nagging" her about it even when she was young?
Re-read it, you'll see. For Sion, he knew already and that girl noble also knew when they were in school, Sion would completely ignore and humiliate her at school too, when she was young and he could've simply had discussions with her and the others. (Just saying, he jumped to the m*rder route way too fast for him to be a normal guy, even we IRL give chances to actual dictators and they remain alive, when he as a teenager is so cruel.)
Actually, her attendant would tell Mia all that stuff but she didn't listen to him so she's still bad for doing this, just want to precise that it's still sadistic of Prince Sion, even when they're wrong, he is also in the wrong, because he never condemned them when he was right next to them, when they all revered him and loved or thought of him as a friend, from fellow royalty he could've said or done something before it all went to smithereens, and if he had done an actual investigation like they're doing now, they would've known the true problems going on.
Mia is still foolish of course, and definitely not adept to be on the throne, though now that she listens to the people around her and that she has actual intelligent and good people around her it's a lot better.