You can get back to the questions
With the DE, there's a reasonably safe bet that the mites and lice are being kept at bay if they're an issue at all, but only a thorough external examination will show that.
Four things come to mind from what I've read here:
A) You could be dealing with Coccidiosis, and it seems to be a regular topic here lately since lots of rain, humidity, and heat create the perfect breeding grounds for the organisms that occur naturally in the environment, the same organisms that chickens pick up while eating from the ground and get infected with Coccidia leading to Coccidiosis. Blood in their stool is a giveaway, but not always. Treatment is with Corid, and more can be found here, but if you're going to treat with Corid, stop giving Vitamin B-1 (thiamine) as it counters/blocks the Corid:
https://blog.meyerhatchery.com/2021/03/what-is-coccidiosis-signs-and-treatment-in-chickens/
B) Worms may be the issue too, or possibly both A & B. You usually won't see worms until it's too late. Once a bird is so overloaded with them, that's when a few slip out the vent during excretion or you might see a load when the bird expires. A fecal float by a vet or someone trained to look for worms/eggs in feces will be necessary. For treatment, most here use Safeguard (Fenbendazole) for goats at a dosage of .23ml for every one pound of bird weight administered for 5 consecutive days - feed directly to the chicken via syringe. Valbazen is another de-wormer that's used frequently...
More on Safeguard here (refer specifically to posts #2 and #9):
https://www.backyardchickens.com/threads/safeguard-dosage.1437427/
C) Egg-bound hen. Have you checked to see if she's egg bound?
D) Reproductive infection in which she'd need an antibiotic:
http://www.poultrydvm.com/drugs/amoxicillin
From what I read, you're keeping her hydrated and fed, which is good. Try to get as much food into her as you can. If her crop is empty at 5pm, it will be empty at bedtime tonight without your help, so feed her as much as she'll eat - she needs the nourishment overnight, especially if worms are eating as well! Get her water too, even better if it contains electrolytes. No treatment is going to help without those.
What dewormer did you use previously and do you have more of it?
Try to get her through the night with some electrolytes in her water and plenty of food, and let us know what her stool looks like as soon as you can.
