This has happened to me on several occasions. My attitude is that if an organisation is prepared to ask for permission and can provide documentation as to the bona fides of the organisation, I grant permission and send a high resolution image if they require it. Just from the details you've presented it sounds like a bona fide request. I would not assume that they've approached you to avoid paying for a photo; there are millions of stock photos on the internet that can be downloaded for free, after all.
But, I must say that I am not obsessive about copyright, not at all - your attitude may be quite different. I have been paid for photos, but I am more than happy to give them to those who ask, and who seem genuine. Of course, there is nothing more unpleasant for a photographer than to see his or her photos presented as being the creative work of someone else; that is fraud, and unacceptable to me.
Andrew the other