Heel mange (chorioptic) - your vet will be able to give you either an injectable, but as said above Frontline spray (as for dogs) sprayed directly into the legs will probably sort it. It is not licensed for goats producing milk for human consumption, but unless you are milking her now she will probably be ok after 5 months...
Eprinex pour-on (cattle version, but there is now also an identical goat version for sale, I suspect the cattle one is cheaper and your vet is more likely to have it) is allso good for it, and it has no milk withdrawal period. Pricier than Frontline though...
I have found it is often an individual problem, even with goats sharing pens on the same bedding, some get it some don't...