Hi There!
I'm so sorry to hear about your baby

I have honestly found when my chickens or ducks appear sick, Bring them inside, give them a warm bath in your kitchen sink or bath tub (the hot water is especially soothing for chickens! it has saved mine when they have gone into shock within minutes they return to a conscious state). When in the bath I take a wash cloth and put it on their back to keep them extra cozy and warm and make sure the wash cloth stays warm with the water. Separate her ASAP from the others, grab a heat lamp, and place her in box without a lid and make it very comfortable and clean. Just simply starting doing that will make them feel a lot better. BYC is amazing - keep posting and I guarantee someone who has been in your s hoes will help out - I wasn't able to read every reply back to you so I apologize if I missed something important. Also, adding apple cider vinegar with the mother in it to her water could be beneficial. Instead of layer feed perhaps give her real foods that provide the nutrients they need. I personally use the Nutrena brand for feed and to me nothing else compares, it smells good, and my entire flock gobbles it down. They also free range from sun up to sun down, and I offer bugs and scrambled eggs 1-2 times a week as a treat. I haven't had to use oyster shells, grit, etc. for my flock. Chickens are also smart, they will eat what their body is in need of. You and your chicken are in my thoughts!!! Please let me know if there is anything I can do to help you out. I will try to find some posts on similar problems for you.