Is German Highschool chill?

I'm 19F from Asia. I'm going to Germany for tip this December. I'm visiting my German friend.

She suggests I attend her high school art class and English class just for fun for one day so I can see what's it like in German Highschool. She said those two classes are very chill and she will ask the teachers permission beforehand.

It's life time opportunity to attend other countries school and see its natural view but I'm worried that it's very rude.

I don't want to be a rude Asian to them😭 what do you Germans think? Is it a bad opportunity?