It's a fantasy novel. Just like someone else here wrote a Martha Stewart prison story with a slight change of her name. By your logic, Martha is really innocent (she is only guilty of being stupid), noone should write a story on Martha and yet there is some member here wrote a story on her.

I was surprised that if Corby didn't use the drug or nor never use the weed before, she should strengthen her case by doing a drug test, proving that she never use weed before. But I don't recall the defense use that as evidence.