Does your hen look as if she is wearing over-large carpet slippers? If so she might have Bumblefoot.
Bumblefoot normally starts out with a small hard black spot or raised rough patch on the bottom of the foot. In extreme cases all the toes and even the lower part of the leg can blow up like a balloon. The cause is usually a small puncture wound or cut from the rough edge of a perch or an accidental landing on a sharp stone.
The condition doesn’t seem to be painful but this can vary from hen to hen with some hens going lame. The tissue becomes inflamed, pockets of hard pus build up and often the only way to resolve the condition is with surgery. Some hens can improve with antibiotic therapy and soaking the foot in Epsom Salts. Exercise will also help.