So the time has come to divide the garden up so she has access to the top part only.
I have planted a Yew Hedge. I was just in time to purchase the last of the bareroot plant and I have chosen Yew because it is evergreen, you can prune it hard and it should only need pruning once a year once it is established to the right height.
We have some chestnut cleft fencing which is 3ft high to stop her having access whilst the hedge grows.