I can breathe for the first time

As I type this... my cat is staring at me from the chair arm. 

I locked her sister in the shed today, because they had both stopped using the cat flap; I figured if i put one of them in there; she would work her way out, and the other one would see and use it too. 

Half an hour later, she had not come out, and i had to go in to find her. 

she was hidden right at the back.  So i thought, well she obviously knows what she is up to. 

so I left her there again. 

When I went back out after dinner... she was gone. Got out obviously. 

Or hid somewhere really special.