Could be an infection like what they get on their feet called bumble foot which is staff infection . Get some Epsom salt and mix with some warm water to dissolve have her stand in this holding her so she stays do this till you can peel off the scab easily might take a few days. There should be a pus plug inside that can be picked out with sterile tweezers. Then keep soaking and keeping it clean till healed. If it doesn't get any better then she should be on an antibiotic. Main thing is not letting it go systemic. I make my ES solution pretty strong at half cup to half gal of warm water put it into a bucket place both feet into the bucket it's easier to keep them in with both feet in.