My neighbor is eighty years old. he left and asked me to feed a feral cat he used to feed?

The answer is patience. Only put out dry food every day--always the same type. The cat will refuse to eat at first, but when it's hungry enough it will eat it. I realize you think this will starve the cat, but remember: feral cats survive because they know how to eat mice, bugs and other wild food. She won't starve.