Can the cage just sit on the garage floor or does it have to be elevated like I have read somewhere before. The wires seem like they would hurt her little feet to stand on if sh were elevated?
Bare wire encourages the circulation of air, which in turn cools her belly and stops hormones, thus stopping her broodiness more quickly. It doesn't hurt them to stand on wire--people raise quail on wire all the time, and I keep some of my breeding stock in rabbit cages when I want a particular pairing. They go pretty freely between the little wire run and the wooden doghouse. Obviously, your wire floor should have decently fine wire (1/2 inch is acceptable, 1/4 inch is better.)
Last question, her head feathers are then and grey and her undercoat is grey, is this normal or is there something else going on. She is a solid black silkie normally.
No idea. How old is she?