Comment by Ish on I'll Become A Villainess That Will Go Down In History ― The More Of A Villainess I Become, The More The Prince Will Dote On Me - Chapter 11

I'm assuming she set up the kidnapping and that her goody two shoes ditzy air headed persona is all an act.

It would explain where a bunch of random kidnappers got their hands on a magic suppressing collar.

However if the two points above are true then I'm not sure if this is the true persona of the heroine or she's a reincarnator too.

They didn't out right say it. It's like they suspecting her. 

Duke was Hella mad tho. 

Also prepare to be extra mad at her brothers

It's not clear due to translations. But the heroine has either been consciously or sub-consciously using charm magic on those around her turning their brain into mush when it comes to critical thinking. Not sure why some are resistant to her effects while others are not so much.

According to those who read further she is a genuinely good person. But from what I can understand from context, her magic ends up creating an echo chamber around her thus she was never able to properly mature since no one ever disagreed with her.