So sorry sararoni, you have done so much for this little one, I know the thought of letting go is hard. I have a two year old RIR hen that is internally laying, with not much to be done for her but keep her comfortable. Although we have lost a few young chicks, we haven't had to put one down before, and I'm honestly not sure I can do it if it gets to that point. I wish I had something else that would help, but it does sound like you have done pretty much all that you can. Good luck.