First, soak for fifteen minutes in warm Epsom salts with a dash of dish detergent in it. Then dry it, and pull off the black scab. This is to expose the wound so you can cleanse all bacteria off. Use saline or Betadine or soapy water.
Next, use Triple anti-bacteria ointment or Neosporin on the wound. Place a non-stick gauze pad over it. Then wrap the foot securely but not so tight it cuts off circulation. Use Vetrap, an elastic stretch bandage you can buy at any feed store. Be sure and get a color complimentary to her coloring. This last part is optional.
If you cut a twenty inch long piece, then cut it into one inch wide strips, it's much easier to wrap a chicken foot. Begin at the shank, winding down toward the toe, then come back up to where you began and press the end firmly to the bandage underneath so it sticks. If you end it at the back of the leg, it's harder for her to work it loose with her beak. This should keep all dirt out so she can go right back with her flock.
Check it in two days and report back with a photo and description of how the wound is doing. We'll judge if it needs more soaking.