Older cat constantly yarling/meowing for food?

Sounds like worms, thyroid imbalance (very common development in older cats) or possibly some degenerative digestive disorder, may be having diahorrea (sorry cant spell that word) and not absorbing the nutrition of the food. You could try a general wormer and if she's still attacking food lilke she's starving, take her to the vet for tests to identify whats going on.