Probably the rust, just to be sure can you rub the hair backward on her toes to check the skin and base of the nails. Skin and nails should appear clean an healthy under the fur, not flakey, red and inflamed and no sign of hair loss.
CLR is Calciun, Lime, Rust remover. You can find it at safeway and home depot. Stores like that..(Lowes, Rite aid, Ace hardware). It would help get your cage into a better condition.