77horses...I just read your entire thread and I think you are a good mommy to your chick. You took the time to ask questions and followed the excellent advice everyone gave you. Sounds like you really love your little chick. You just didn't know any better. My Aunt never fed her chicks or chickens anything except "scratch" and they free ranged and did just fine. Her chicks were raised by their mother hens and started out on ground corn and whatever they found free ranging. Being a "house chick" is different, so are some chickens kept in a coop with a run. They don't have the variety of natural foods to choose from, so have to be given a good, well balance, nutritional feed. That may be why your families other chicks and chickens did fine with a supplement of cracked corn.
Kudos to you for wanting what is best for your little chick, and taking the time to research and go get what she needs.
BTW....if you have trouble switching her over to the chick starter, try mixing it with a little water and egg yolk at first. Then you can decrease the water and yolk a little at a time, until she will eat the crumbles alone. That's what I had to do when I adopted 3 of my Aunts little bantam chickens who were used to only "scratch" and free ranging all day. They wouldn't eat the layer crumbles at all at first. It worked well for me.
She won't even need grit with just the crumbles and yolk. You will only need grit, sand, of very tiny stones from the yard if she eats any other treats, whether from the house or vegetation and bugs from the yard.
Good luck with your baby. She should start picking up weight, size and feathers within a couple weeks. You are on the right track.