What should I give sick chicken to make her gain weight?

[treecow]

One of my Buffs has lost so much weight these past two weeks because of a mystery illness so we took her to the vet and he gave her some shots but he said she would probably die in a day. He didint know what she had either. Here she is four days later, and skinny. She won't eat much so I wanted to make sure that everything that I give her doesn't go to waste. Is there any food that is fattening and nutritious that I could give to her in addition to her mash.

 

[Judy]

A little yogurt on a scrambled egg would be nutritious and are usually things they like well.