There IS Something you can try Immediately for Nourishment but will cost a little. FIRST,GET HER INSIDE & PUT HER IN A TUB AWAY FROM THE OTHERS. They will pick on her & Stress will only make her go down faster! BUY ORGANIC Coconut Oil sold at places like Sprouts is good for MANY REASONS! FIRST, its high in fat & will give her energy,2nd. IF she has an Intestinal Blockage it may help release it,3rd, THE ORGANIC (I prefer the Brand "Jarrows") has a natural ingredient called Caprylic Acid. IF its Fungal it will treat Fungal Masses,Aspergilosis, & pretty much Anything Fungal. I have been using it for Fungal & it has saved my Birds. I had to use MEALWORMS & Coconut oil since I had to get them away from the Grains. They wouldn't really even eat the Pellet or Crumble since it was too hard to digest. You can even Force a little. When you chill it gets hard so you can try chunking it into sm. pieces but use a knife & then dump it in a bowl or plate. To get it solid quick just throw it in the Freezer for 5 -10min. IF YOU CAN get Mealworms Dehydrated or BETTER the Real at
Petco.
They usually sell them in a sm. frig in the Reptile area & you can get 100 for $5. Its GOOD Protein & ALSO HIGH In Vitamin A & Omegas which IF there is Fungus somewhere then it will be a dbl. punch of goodness. You May Contact me with questions if you would like. I have dealt with enough issues & have learned a lot over 10yrs.
IF SHE GOES BIG FOR THE COCONUT OIL then watch her fecals. Feel her abdomen for harness,distension,etc. ALSO Check the Crop Thoroughly for Any Bumps or masses, They will starve themselves if Fungal. You also "May" want to chop up VERY sm. bits of Grass(not Drenched) & see if she goes for it. They like Grass for Intestinal issues/Fungal.
You mentioned it was drizzling. If you are having back & Forth weather (wet then warm) you may be dealing with a Fungus or Coccidiosis.
A GREAT SITE IS "Poultrypedia.com". There is a LOT of good info. on Diseases,Drug Treatments,& Fungal Infections.
Good Luck & God Bless!