1 1/2 weeks is a really long time to be sick in chickendom. Puffing up means "I do not feel well" - years ago I had a roo do this and the stupid feed store told me it was just how they keep warm - they gave out misinformation and my poor roo died.
Isolate her so you can observe her eating, drinking, pooping, egg laying (or lack thereof). If she will be stressed away from her buddies, set her up near her buddies in a really comfy large dog cage with lots of pine shavings and fresh food (not just layer food - try some scrambled eggs, warm oatmeal, sunflower seeds...whatever she really likes)and water. Report back on each of these things (eating, drinking, pooping, egg laying) and call a vet with this info if you can. And as noted by previous poster, post photo of poo if you can.
Have they been wormed and if so, when and with what? She could be eggbound but it could also be any of a number of other things. I had a hen go lethargic last Labor Day and rushed her to vet same day - blood work was consistent with infection/inflammation from unknown cause. With meds for these things, along with tube feeding by the vet she bounced back quickly and has been her happy self ever since. The vet and I never knew what hit her but were pretty sure she would have succumbed without the meds.
To bolster her a bit, give 3 drops liquid Polyvisol childerns vitamins daily, dribbled gently along her beak line with a dropper so she swallows on her own and doesn't choke.
Have to head to work but keep posting with updates and pics etc. so folsk see your posts and can weigh in. I hope things will work out for your ailing hen.
JJ