It won't hurt to treat for coccidiosis. It's a problem in spring if there's been moisture and above freezing. The population may be heavy. I would treat the entire flock, and give the sick hen a Corid drench for the next three days along with the Corid water.
Get liquid Corid from your feed store. Mix two teaspoons into one gallon of water and give it to the flock each day for five days as their only water source.
The drench will be just for the sick hen. Give .1ml per pound of body weight undiluted directly into the beak once a day for three days along with the Corid water. Mix the Corid water fresh each day. After five days, stop the Corid, wait a week, and do it again for five more days. No need for the drench this time.
Meanwhile, check the crop of this hen in the morning to see how well her crop is emptying. If it's full after not eating all night, she may have a crop disorder that may need treatment.