If you haven't used .Flubenvet so far, then you should give all your hens a course as soon as possible because all of them will need it, even if apparently healthy. and thereafter treat them all every 4-6 months. Its easy to administer, just add a measured amount to a weighed quantity of pellets, using the measure provided in the packet, and then feed only these treated pellets for seven days. Don't give anything else, so each hen will eat the full dose she needs according you her weight and appetite. A pot of Flubenvet treats 20 birds so will last more than one time if you have fewer than 20. You can buy it online and there's no egg withdrawal problems.
Unfortunately it may be too late for your poorly hen. I agree with Chris and Cab that you should either take her to the vet if she is very special to you, (though this may be a costly way to find out that nothing can be done to save her,) or cull her, especially if she is an older bird.
All hens get worms and their health and productivity depend on your controlling them. See this article in Poultrykeeper for more information on worming http://poultrykeeper.com/general-chickens/worming-chickens
Also, please read this article, about using antibiotics on chickens.
http://poultrykeeper.com/poultry-medication/antibiotic-use-in-back-yard-poultry