Chicken with open mouth/weak/losing weight

[Brenee06]

Hi guys! Was hoping someone could help with this. My girl Elvie has been walking around with her mouth slightly open. When she makes a sound, it sounds like a whistle. She more boney than my other hen and she has stopped laying eggs for a week now. Previously, her eggs weee coming out so thin on the shell, that he would just shatter when it hit the floor. When she poops, it comes out white and milky. Her poop tends to stick to her feathers in the back. She is also lethargic and won’t even run from my young boys now when they come around. I tried to find a good video to show her sound but it’s hard to catch. Any ideas how to help her?

 

[Brenee06]

If you listen carefully, you can hear the high pitch whistling