Are you saying that you only feed your chickens once every other day? How many chickens do you have and what is your climate and forage conditions like? Feeding too little can be as bad as feeding too much. If you are in a colder climate going into winter there will be very little for them for forage on whilst ranging. She might have been tempted to eat grass and hay if she didn't have access to any other food source and this can sometimes cause an impaction. Her crop doesn't look huge in the video and she is nowhere near the size I would expect of a 4 month Cornish cross. What does her crop feel like?
What do you give them to eat?
My gut feeling is that it is Marek's from watching the video but not absolutely certain. I would see if you can tempt her to eat some scrambled egg and put a multivitamin supplement in her water or give her a direct dose. You can also make a chicken sling/hammock to support her weight and keep her in an upright position.... they can be made from everyday items....
You can clip little empty yoghurt pots to the front for food and water, so that she can reach them from her hammock.
What do you give them to eat?
My gut feeling is that it is Marek's from watching the video but not absolutely certain. I would see if you can tempt her to eat some scrambled egg and put a multivitamin supplement in her water or give her a direct dose. You can also make a chicken sling/hammock to support her weight and keep her in an upright position.... they can be made from everyday items....