Hen won't eat,what could this be?

[Lnzsmith]

Our 2 yr old Lavender Orp won't eat. She went off her feed about 5 days ago. She had diarrhea overnight in the coop and just kind of stopped eating. She is fairly active, does scratch a bit around the yard, but we are giving her electrolytes and yogurt to keep her strength up.
Treatment tried: Wormed flock with safeguard (once, to repeat in 10 days per instructions for roundworms); CORID treatment in water and two days of beak drench (she almost died from cocci as a pullet), changed to new bag of feed, have bathed in epsom salts (she is pretty nasty bottomed).
Odd things observed: She has roughed up feathers on one side of her neck, but no sign of injuries or pecking? Stools are liquid, mucousy and white mostly although today first stool had some solids. She had a slightly swollen belly the first day but it's normal now. No straining. Hasn't laid but isn't a really great layer.
We hand-raised her and she is a beloved pet, often first out in the morning and goes to bed last of all.
We're worried/don't know what to do next.

 

[Wyorp Rock]

had a slightly swollen belly the first day but it's normal now. No straining. Hasn't laid but isn't a really great layer.

I'm sorry she's not well, can you post some photos of her and her poop?

She has laid and egg - when was the last time she did?

Is her crop empty in the morning before she eats/drinks?

The swollen belly and not laying eggs - the first thing that comes to mind would be a reproductive disorder - possibly internal laying, peritonitis, salpingitis, etc. If she is still somewhat in lay - have you felt inside the vent just to be sure there is no egg?

 

[Lnzsmith]

Well, today she seems fine. I swear, last night we thought she might die. Just really listless and weak seeming. Today she ate and drank and hung out with the other ladies and had fairly normal poop. ??? What the actual heck? I was really worried! We'll see what she does tomorrow. I am wondering about some sort of accidental ingestion of something poisonous?
(She has been known to peck at mushrooms in the yard...)

 

[Wyorp Rock]

Well, today she seems fine. I swear, last night we thought she might die. Just really listless and weak seeming. Today she ate and drank and hung out with the other ladies and had fairly normal poop. ??? What the actual heck? I was really worried! We'll see what she does tomorrow. I am wondering about some sort of accidental ingestion of something poisonous?
(She has been known to peck at mushrooms in the yard...)

Our Lavendar Orp (2 yrs old) had an episode about 5 days ago where she seemed to have a gush of fluid, egg white like, before she came out for the day. Then she seemed ill.

She seemed better for a couple of days, no more nasty bottom, but today she doesn't seem well. Lying down, eyes closed, not eating or drinking. I am at a loss. She's not a big layer and hasn't laid since her last (hard) molt earlier this spring.

https://www.backyardchickens.com/threads/lavendar-orp-suddenly-ill.1392202/
I just saw you had another thread from Monday. The symptoms you describe there (quoted above for reference).
I would suspect that she has a reproductive disorder.

She hasn't laid an egg since molt, the gush of fluid/egg white like and then she was ill. She felt bad, but then got better.
Then she felt bad again, now is better.

She may be internally laying or have something like Peritonitis. The gush of egg white - she may have had a soft shelled egg but the membrane broke before it was laid - either the membrane was not passed at that time or once expelled another hen ate it quickly, she may have passed it later on and another gal grabbed it.

Anyway, with those symptoms I would suspect a reproductive disorder. Sadly, these are common in laying hens. I would observe her for a few days, if she has another episode, then see if there's more discharge like whites or yolk, if she feels really bad, then I would think about giving her an antibiotic. This is not a cure, but a supportive measure to help fight infection. Egg yolk/white that is released into the oviduct and/or has traveled back up the oviduct into the abdomen can cause infection. An antibiotic can help with infection, but a lot of times it's a short term preventative measure.

I would still check her over for lice/mites, consider getting a fecal float to check for worms as well. If she's not feeling well, then a lot of times they are more susceptible to parasites taking advantage.