... It’s on her right side, but it was so big that it took up both sides. I have given her some plain yogurt and cooked egg yolk and water wit ACV. Hildegard fell asleep on my while she was perched on my fingers, laying on her back. When she woke up she pooped twice and climbed onto Scott’s shoulder and then chased our cat around.
I will wager a dime against a dough-nut that what you are seeing is your chicken's crop or craw, a.k.a. the 1st of two stomachs that all chickens have. Your Isa Brown sounds too full of its self for there to be much wrong with it. If the lactic acid in yogurt. and the acidic acid in ACV doesn't kill your chick then nothing likely will.
I direct your attention to the chick in the Purina add in the right hand border and its bulging crop.