Basically prison for the rich and nobels. I think she is in there due to taking the blame for something her brother had done or that's what I at least think it is due to the clues I've seen.
It's already explained why the prison is flexible.....
I mean overall it's not that different than jail irl. Prisoners who behave good and those with connections get special privileges. Even irl prisoners can spend their time in the courtyards, have a hobby, work, etc. It's really not that far-fetched of an idea to think of a prison for nobility that's more lenient.
at first i like it, but the more i read it the more i confuses cuz idk why she there , idk why prison can be so flexible