The Corid won't hurt her. Dosing will be below.
I looked at some of your previous threads, could she be the one that expelled a lash egg back in January or did you figure out it was a different hen?
I would suspect something reproductive going on, but it's so hard to know for sure. I'd think about getting extra Calcium (1Calcium Citrate+D3 tablet daily for a week), deworming her (Safeguard or Valbazen) and giving a round of antibiotics (Amoxicillin or Baytril) to see if that helps.
Since you are waiting on the vet, that may be best.
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Liquid Corid dose is 2tsp or Powdered Corid Dose is 1 1/2tsp per gallon of water given for 5-7 days as the only source of drinking water.
Do not add any extra vitamins/electrolytes that contain B1(Thiamine) to food or water during the course of treatment.
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You can find Calcium Citrate with D3 in the vitamin aisle of stores like Walmart, CVS, etc. Give 1 tablet daily for a week, just pull down on her wattles, pop the tablet into the beak and let her swallow.
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To treat most worms that poultry can have except for Tapeworm use:
Safeguard dose is 0.23ml per pound of weight given orally once a day for 5 days in a row.
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Valbazen dose is 0.08ml per pound of weight given orally once, then repeated in 10 days.
A couple of previous threads that stood out:
https://www.backyardchickens.com/threads/bright-green-poop-help-please.1634343/
https://www.backyardchickens.com/threads/lash-egg-in-water-bowl.1609582/