As was suggested earlier, ensure she is wormed with a wormer from the vet, not a pet shop.
If worming is up to date, then this may be learned behaviour: she has learned that when she miaows in a certain way, you give her food. If you stop responding to her demands, she'll stop demanding. Feed her at set times so that she learns that no amount of howling will get more food from you. She'll learn and stop bothering.
It's a bit like those tests they do with rats when they give them a choice of "taps" one of which gives them sweet water, the other gives nothing. After a while, they stop nudging the one which gives them nothing.