Dropping feathers can sometimes be stress induced.
Is she in that bad of shape or is she being picked on that she needs to be quarantined?
I usually leave my hens with their flock so they can live as normally as possible while I treat them.
In the photo she doesn't look too bad. If her...
A lot depends on what's going on.
Sometimes an antibiotic can help offer some relief. If there's fluid in the abdomen, draining can offer some relief. There's no cures for reproductive problems, just supportive care.
Photos are always welcome.
If possible, take a sample of her poop in for testing. If she does have worms, then you'll want to treat with an anthelmintic. Sadly, a lot of the natural remedies are not that effective.
I'm sorry she's been sick for a while, sometimes they can have good and bad...
Oh good, what dewormer did you use?
Sorry that she's not been well for a while, often laying hens can have reproductive disorders which can have other symptoms accompany them.
Poop has a lot of urates in the first which can be from not drinking enough. The other, it can be from a number of...
When was her last egg?
Any swelling or bloat of the abdomen below the vent between her legs?
Have you dewormed? Take a sample of her poop to your vet for a fecal float, if possible, to rule out worms being part of the problem.
The article below is helpful when addressing crop symptoms...