Gaping silently at night sounds like a respiratory illness or perhaps a crop issue. Can you check the crop to make sure its emptying overnight? Any symptoms like coughing, sneezing, mucous, bubbly eyes? Is there a strong ammonia odor in the coop?
Birds with Gapeworm will gape continually at all hours, often they will cough or make a strangled cough/sneeze type of noise to see if they can clear their airway. They seem to be in respiratory distress and stop eating/drinking because of the constant gaping.
Check your hen for any bloat or feeling of fluid in the abdomen and for lice/mites too.
If she is still not better after checking her over, start your own thread in the ER section giving details of treatment(s) you have given along with symptoms and the timeline of symptoms.
Photos of her and her poop may be helpful. If she's gaping and/or making noise at night, a video of those actions can be helpful too. Upload video to youtube and provide a link or add your video to the BYC Gallery and let us know where to find it.
Calcium it certainly not a cure all, but it can sometimes help a hen that is having a hard time expelling an egg or lash material through crisis.
