Vermex may help as a tonic, but is not effective at actually killing worms and their eggs. To be sure they've been dealt with, you really do need Flubenvet, which has been developed specifically to treat the problem. So whatever is wrong with your bantam it would be a good idea to worm the flock. You can buy a tub of Flubenvet online and add it to a measured quantity of layers pellets, then you just feed them that for 7 days and each bird will eat the right dose for her size. A pot will treat twenty hens, and the remainder will keep until the next time. You can buy Marriages pre-treated pellets but you'll probably have some left over which will be out of date by the time you next need them.
Maybe there's nothing wrong with her, it's just her way of being vocal! But worming every 4-6 months is really worthwhile all the same. You can still use Vermex in between if you feel it helps.