If they are on a low Income CP would help with a neutering voucher and may even be able to take her in so she can go to a home as the bit about struggling to feed her makes me a tad worried what about injections, flea treatments worming etc, its not just the case of feeding as well all know how expensive that can be and I know more than most on the food and vet bill front
The vet if part of the CP scheme and explaining the circumstances should do it at the CP voucher rate - I know I get my ferals done at that rate when we are trapping and also get discount on the wormers, injections and worming treatments may be worth asking if they would do it at cost due to the circumstances