Ferret litter box problems

Hi all! I just got my ferret and she was using her litter box like a champ! I'm home with her most of the day so I clean it just about everytime she uses it! Well then today she has decided to start using the shelves in her cage as her litter box! As I'm cleaning he litter box she used the shelf right in front of me!! How do I get her not to do this? Lol any advice would be great! 

When I got my babies, I was told they were litter trained. They were, but once they were re-homed to me, the change in scenery made us have to start from square one. If you already have a low corner litter pan with dust-free/clay-free litter, the best thing to do is monitor her. When you see her squatting to "go", quickly move her to the litter box, even if its too late! have an extra litter box outside of the cage for the same situation during play time. make sure to reward her when she makes it in!this worked within 3 days for my ferrets.