Ludwig was the one and only person to ever admonish her in her whole life. Her father doted on her so much that he would cut down a whole forest just to give her some gifts. Everyone buttered on her just to throw all blame on her when something went wrong (the nobles lied and convinced everyone that Mia ordered them to ruin Tiona's dress and locked her up). The only reason she wasn't punished right then and there is because there was no proof (and how could there be one when she didn't do it in the first place?)
Worth to note that in the previous timeline, she met Ludwig only after she dropped out of school and the empire had collapsed.
All she needed was someone to point out that she was a selfish princess and that she could do more in her position. But the only thing that people cared was that she had to be executed to make them feel better.
Seems I was wrong about Ludwig a bit, sorry about that.
I still don't think it would help much.
By the time they might try to warn Mia, the big three (prince, Tiona, and Rafina) already has a really bias view of her since she bullied Tiona, and from their POV, even go as far as locking her up on a tower at one point.
Her past-self response when hearing about that incident on ch. 10 is also "Isn't it merely natural for nobles to do as they please to commoners?".
From a relatively unemotional, third-party view, it's easy to say she doesn't know any better, especially since "she's just a kid". That's not something you usually could do from involved parties with similar age. If I was them, I probably couldn't see her as anything more than someone born evil.