What do you feed including treats (quantity of treats)?
How much space do you have for how many chickens? (sq ft of coop and run)
It's hard to know why she's picking at her feet - could be nutritional/vitamin deficiency or stress (psychological stress).
I would soak the feet in a warm epsom salts bath daily to help them heal. Apply a little Vetericyn, triple antibiotic ointment or Blu Kote to the feet. Ideally, she should be kept on clean dry bedding.
Try increasing her protein (chick starter, flock raiser/all flock, egg, meat, fish) and limit the amount of treats she eats. I would also give a poultry vitamin that contains B vitamins (like Poultry Cell). Direct dose is 1cc per 3 pounds of weight.
Look her over well for lice/mites on the body. It's hard to see the other foot, but the scales don't looked too raised which would indicate Scaly Leg Mites which could be another reason for picking at the feet - those can be treated with vaseline or oil rubbed into and under the scales of the legs and feet.