Thank you for the additional info. It appears we're in different time zones.
The fluffing you describe is common when any bird is feeling 'off' or ill. They tend to lose body heat then and by fluffing they create a remarkable self-contained blanket, a way to hold in and circulate their own body heat. By becoming lethargic, sleepy, they save energy and lower their metabolism. The equivalent of a very sick human taking to bed for a few days.
In many cases a bird can fight the effects of an illness and let it run its course, just that human would. However, in about as many cases, the bird needs help.
This could range from being kept in an 'hospital' environment that you can set up with a warm enclosure and low activity levels, good feeding and hydration; to having to administer appropriate drug therapy depending on clinical findings by your veterinarian.
Dystocia is the obstruction of oviposition or cloacal function because of the egg in the distal oviduct. It is slightly different from being egg bound - which would have very likely taken her life in this amount of time.
As this obstruction worsens it may crowd or impair the air sacs or lungs and you’ll notice difficulty breathing. In any event, your hen would need medical attention and possibly surgery.
In the meantime, let’s try to increase the humidity in her area. Install a vaporizer nearby for a good amount of steamy moisture in the air. Make sure she has plenty of fresh water and feel free to offer her some Gatorade (preferably without sulfites and without added zinc) - or children’s Pedialyte. An eyedropper just inside the beak, a drop or two at a time (slowly, not forcefully) may be helpful in keeping the bird alive until medical intervention.
A remote possibility for these symptoms may be EDS (Egg Drop Syndrome) which has become quite a problem since transitioning from just ducks and geese (it's believed through an infected/contaminated vaccine). Transmission can be through the feces of chicks hatched with it, from other infected chickens or environments.
All breeds of chickens are now effected, but it appears more often in broilers and brown-egg layers.
Cessation of laying occurs or abnormal eggs (no shells, thin shells). Usually there's the bad eggs leading up to the stopping of laying altogether.
Diarrhea is also usually seen.
The good news is that production often restores after a molt.
You may also be seeing a non-bacterial respiratory infection, even though you might not see exudates and what we'd typically associate with respiratory distress.
In any event - since you have a flock to protect - whenever just one chicken is ill it's best to have that one separated and diagnosed. By waiting, even if you see recovery, you might be returning a carrier to the flock environment and the next fowl to become infected might not be so lucky.
You've done all the right things - I really hope this is nothing serious and you find all smooth sailing ahead.