She wants us to leave the window open all the time. We want her to use the cat flap. Obviously we are losing. 
We've tried putting her through - and won't be doing that again. She was really pissed off!
We tried feeding her toys through.
We tried having one of us either side, passing things through to each other.
We tried standing outside and pulling a piece of string through.
We tried propping it open.
She stands and looks at it but refuses to go through it.
Any ideas?