Cat scratching a particular place persistently

Question
One of my cats is 3 years old. Approximately 1 year ago she got a scratch on her cheek from her sister, which she wouldn't let heal, persistently scratching everytime it scabbed, until it was much larger and our vet advised us to put a cone on her and put her on antiobiotics, something to calm her down and something to relieve any itching of her skin!
Since then we have been in a cycle of putting the cone on and keeping her in for 2-3 weeks, until the sore has healed, the skin and fur has grown back and you cannot see the original spot - then we take the cone off and within a very short period of time she has usually scratched the area again. Often it loooks even worse than before.
Putting on the cone just does not seem to work, other than to stop her scratching;but of course her claws are much sharper,because she has not been allowed out, and she wants to clean herself vigorously, having not done so for some time!
The vet has examined her skin - no parasites are evident, so he doesn't think she has an allergy - he seems to think she is doing it for attention or because it is a habit now, so the cone is put on to try and break this, but it doesn't seem to be getting to the route of the problem. I don't think this area of skin is particularly very itchy for her, as she doesn't automatically scratch it as soon as the cone is taken off.
I have asked numerous people who also have cats and no-one has ever come across this sort of behaviour. I am at my wits end to try and find an explanation/help for her. I hate putting the cone on her as it is cruel, it doesn't seem to be solving the problem, it seems to be a relentless circle now, it doesn't really help the relationship between my two cats (as the other one is frightened when she has the cone is on)and I don't know where else to turn for advice. A cat's life is relatively short and she has spent the best part of this year in a cone. I have searched the web for any similar problems to no avail and hope you can perhaps shed any light on this and suggest a way forward.  

Answer
If it is itchy, then she should do well on either cortisone or antihistamines when the cone is off.  However, it could be behavioral in nature and for that either elavil or buspar may help. It  may take a few weeks of each drug to see what works and what doesn't.  This will require your working with your vet to find out. If all else fails, ask the vet to do a skin biopsy to be sure what the disease process might be.