Can you take a fresh sample of poop to your vet for testing of worms and Coccidiosis?
Safeguard (Fenbedazole) is a de-wormer. This should take care of most worms. Dosage is 1/4 ml per pound for 5 days in a row. Keep in mind there is an egg throw away period - generally that would be 14days after last dosage is administered (at least 19days all together - if you worry about drug residues, throw the eggs away for a longer period of time or research FARAD for timetables).
Corid (Amprolium) is used to treat Coccidiosis. Dosage is 1 1/2 teaspoons Corid powder per gallon of water or 2 teaspoons of 9.6% Corid liquid per gallon of water.
Give for 5-7 days - make sure this is the ONLY water available during that time period. Mix a fresh batch at least once a day. There is no egg withdrawal period for Corid.
You could treat for both at the same time if you feel it is absolutely necessary. I have found not contraindications between giving Amprolium along with de-wormers, but I am not a vet, so it's always best to consult a medical professional when giving multiple medications.
As always, once you finish a course of treatment, it's a good idea to offer poultry vitamins and probiotics for a few days to help restore the gut.
Give your hen a good going over. Worms and Coccidiosis can both cause weight loss, but other illness and disease can also cause the same symptoms. Check her for lice/mites, see that the crop is emptying overnight, feel the abdomen for any bloat/swelling or feeling of fluid (reproductive and internal laying disorders are notorious for weight loss in laying hens), disease like Marek's can also cause wasting as well as poor nutrition.
Keep her hydrated and eating the best you can. Sometimes a higher protein feed (chick starter or flock raiser) can make a difference. Other options would be to offer a little chopped egg or meat in addition to her normal feed.