I am very sorry to hear about your hen. It's hard when one has gotten close, caring for a bird.
In regards to acclimatizing, our ideas differ. In my experience, it takes longer than this with the birds I've dealt with. I generally don't bring in live birds, but for the ones that have been brought in, they're in quarantine for 1-month minimum at a different location in an enclosed space before eventually being exposed to the litter from our flock for an extended time before they set foot on this property. This sweetie required 2 months to change from the first picture to the second picture and before I felt confident she was in the condition and health to be gently exposed to our flock. She was integrated while in her kennel for additional time before she was allowed to be fully released into the flock.
View attachment 2371396 View attachment 2371394
She was sent home with me when I delivered guineas. She had been purchased in a trio at a poultry sale but had not integrated well into their flock and they thought she'd do better in my flock since I have small and medium-sized birds. She was wild, stressed, pale and lacked comb development for a year old plus bird. She has never integrated into this flock; she won't associate with other birds and won't go outside unless I take her out of the coop. She associates me with food, water and protection and runs to me to be held when I enter the coop. The only time she lays eggs is when she's in a cage in the house over winter where she feels secure and comfortable. I included this to give context; she was acclimatized and not in moult when I got her.
I do not share the opinion that intensive livestock facilities are horrible and cruel because I've had the experience of working in one. It is different; every method of caring for animals has its pros and cons. However, hens don't lay well if they don't receive a high level of care. If these hens had not been healthy or laying well, they would've been culled. Chickens moult and reduce or stop laying eggs at this time of the year. For a farm in the business of selling eggs, they replace hens in moult with young hens that will lay consistently so they have product to sell.
We are experiencing similar temperatures to yours and the majority of my free-range flock has been staying inside their coop. I have birds in mid moult that are experiencing a lack of feathers and look rough. Most of my flock has stopped laying as expected. The young hens hatched earlier this year will begin laying soon. Free-range or intensive livestock, it's much the same. I wish you the best with your remaining hens.