You isolated her because she's being picked on or it's just easier for you to access her for a few days?
I would expect a crop to be firm/full after a day of eating and foraging. Check first thing in the morning before she eats/drinks to make sure it's emptying.
I wish DE was a dewormer, but sadly it is not. The benefits are debatable and you can do your own research on that. For deworming, you will want to use an anthelmintic like Fenbendazole (Safeguard/Panacur) or Albendazole (Valbazen). These 2 will treat most worms that poultry have.
There are numerous reproductive disorders that can affect a laying hen. Egg binding is when an egg is stuck or bound in the oviduct, this is usually an emergency and the hen would be in distress in a short period of time.
Cancer, tumors, Peritonitis, Salpingitis, Internal Laying, etc., are all common reproductive issues that can affect laying hens. These symptoms of these conditions can be quite subtle in the earlier stages. Most often you will see a hen start to slow down a bit, their production may slow or stop as well. There is no cure for any of these disorders.
Supportive care can be given. Make sure she's eating and drinking well, deworm, check for lice and mites and see that her crop is emptying overnight. Address "treatable" symptoms as they arise like a slow or sour crop, worms, parasites, etc. Leave the hen with her flock if she's not getting pecked on and let her enjoy life.