So the cat flap has been closed when she has been left alone. It was decided to fit a new cat flap which would operate only for her microchip....voila!!!
It will take her a while to be confident enough to believe that the tom cat is not lurking on the other side waiting to come in and steal her stuff. And she will have to get used to the different shape of the flap entry but it's a relief to us to know that it all works.
A short while later I tempted her out into the yard with a new feather toy and then left her to see if she would come back in through the cat flap.