well at least shes eating. it is probably muscular or neurological. she might bring herself out of it. she probably got into a tangle of wire or ran into something and pulled a muscle. make sure she gets good vitamin supplements mentioned above and she will probably be fine. has she layed any eggs?
you can give them some small live mealworms if you can get any. and once they start growing their big girl (or boy) feathers they can be let outside for a while every day.
shes perfectly fine. sometimes hens burst a blood vessel whilst laying there eggs. and the white crust is probably just some dried poop. it happen to mine all the time. i just give them a little butt trim they dont mind it. as long as she keeps laying eggs she is ok to go back
yes i put a rock in the brooder with them and they loved to cannonball off it as well as roost. i made them a wooden perch when they got more experience with their feet.