I would agree with treatment for this fear - even if there were not cats at your building I am sure you wife comes across them from time to time, in the street, at other peoples houses, on TV etc?
I would strongly recommend hypnosis .... it might sound strange and I know many people are sceptical .... however, I did a self hypnosis courses some time ago and find it very powerful. It doesn't need to be SELF hypnosis though, any good, registered hypnotherapist can help.
The National Register of Hypnotherapists website can help you find someone in your area:
http://www.nrhp.co.uk
Good luck - give it a go.
EK