True, but Oka herself is fake as fuck. Her monologue admitted that her entire persona to her students has always been calculated and fake to the point that she's not even sure what her own personality is supposed to be. It's pretty obvious to the audience and some of the captive students that she's just been manipulative and possessive, wanting to spoon feed knowledge and trivia to her students while being perceived as "cool." It's not quite narcissism, but certainly some kind of self-worth complex.
She's had a notable shift in personality since Shun's party arrived at the village and learned the truth. That cheerfulness she had in Japan and the magic academy evaporated. Just bittersweet arrogance that all of this is "her job to fix." When you think about it, that's not too far from Hugo's bullshit that this whole place is 'his playground.'
The class rep is a good example of finally seeing through her. They went from pretty good friends in Japan to someone who absolutely despises her. The only one who hates Oka more is Sophia.
If she sees most of her students die before they're 20, and sees one that says they live to 500 and is in the demon realm, do you think she's going to tell a lazy pet dragon that they're alive in the demon realm, or pretend that they're dead? Or what if she sees that Shun or Fei die in the demon realm? She will absolutely lie in that instance because she's obsessed with shepherding all of them.
Yes, all of which Potimas is probably taking advantage of.