You did not mean that you put neem oil in their food, did you? I assume that it was coconut or mineral oil?
If they are laying normally, it likely is not a reproductive disorder. Many hens who get internal laying, EYP, or ascites, may have pressure on their internal organs, and that may in turn...
Rather than starve the others, could you keep her in a dog crate with water? I would add electrolytes to the water. Many use refrigerated coconut oil cut into small pieces, and give a tsp of that daily, followed by massaging the crop several times a day. Mineral oil can also be used instead. The...
How does her crop feel? Can you check it first thing in the morning to see if it has emptied overnight. A full and hard or boggy/puffy crop can be a sign of impacted or sour crop.
If she has a respiratory disease from MG, tylosin or Tylan would be more better suited than amoxicillin which doesn’t affect MG. Doxycycline would also work. If it is caused by a virus, it will not respond to antibiotics, but would last a minth or more. You can get tylosin for the water here...