Well that has to be handed down by the courts? It's not a 'law' per say, but something that can be argued through the judicial system, to stop her from profiting from her story.
I can't see it happening though, as there's still speculation over whether she's innocent or guilty and regardless of how any of us may judge her, she has always maintained her innocence - there's also certainly a swell of support and sympathy for her situation from the Australian people.
She's lost years of her freedom and youth. Rightlt or wrongly, once home, I can't see them stopping her from telling her story. She'll make a bloody fortune out of this.
Watch this space...........interesting times ahead.