Thank you for the suggestions and advice.
I did approach this from an OC point of view and I still think it will work with that method IF I was skillful enough.
I probably have instilled the behaviour over the years without realising it and to be truthful it never really bothered me that much, but I do have neighbours who perhaps don't appreciate her calling.
She doesn't scream constantly and just yesterday, when she started calling, I just picked her up, hooded her for a while, then sat her back on her perch where she was quiet. I think the act of hooding interrupted her mind-set.
I think there are plenty of other methods that will work, though when people say hunting will quieten her down, perhaps, but it hasn't made much of a difference that I can tell. Maybe she would be ten times worse if she wasn't catching her own game. She does catch on average 40 head of game a year, mostly single kills then crop up and home.
Again thanks for your suggestions, its much appreciated.