This morning I went out to check my chickens and one of my hens was laying down in the middle of the yard which is unusual for her. She is an Easter Egger and 1 year old this month. I've had her all of her life. She is normally active and will move away from me when I walk towards her. When I picked her up to check her out (normally she would not let me pick her up without a fight) she had yellow fluid come out of her mouth. She was healthy and acting normal last night and laid an egg yesterday that was normal. I have not seen any poop from her today. I was thinking she might have sour crop because of the yellow fluid, but her crop feels completely empty, when I massage it I can just feel grit in there and nothing else. I looked at her vent and it looked pink and normal. She will stand, but gets shaky when she's on her feet. I don't see any signs of injury on her. Her breathing seems normal, and her comb is it's normal bright red. My hens free range in my backyard and they have access to plenty of fresh water and food from several different dishes. I have been feeding chick starter to everyone at the moment with free choice oyster shells for the layers since I have some pullets in the mix. None of my other birds are sick. I now have her separated from the flock in a dog kennel with water with ACV and probiotics. I wanted to get some insight to see if anyone had experienced this and what it might be, and if I should try any other treatments before taking her to a vet. Thanks for any advice!