I offered to give kitten food to a group that I'm on as a way of thanking them for helping me out to get my cats spayed I have already made a £20 donation and they are always asking for donations of cat food and a woman told me that they didn't want it but she could give me their PayPal or bank details so I could donate money and she gave me a list of cat food that I could buy for them. Is it just me who thinks you don't turn down cat food if someone is offering it. I thought I was doing a nice thing maybe IABU.
I had no trouble donating a big bag of the wrong sort of cat food that twit DP had bought and lost the receipt for to our local CPL last year. Your contact at whatever this rescue type place sounds a bit too enthusiastic about fund raising for her own good.
If they're always asking for cat food donations, they surely can't be only accepting one brand. That'd never work. Sounds like they're being precious to me. Have you tried another nearby cat shelter? There will be more than one.
A lot of places tend to use one type & they don't want to be giving animals a variety because it will either upset their stomachs or they'll be having to keep records of who gets what. It's just practical.