That could be ringworm or mange mites, you should get her to a vet in the next couple of days as these things can be very serious, and sadly quite common in fairly new piggies! If she came from an approved rescue you should contact them too, in case any other piggies are affected, and they might help with vet costs- if she is a random rescue from the free ads or someone who couldnt look after her, unfortunately this is just something that happens, but it still needs investigating then treating by a vet... we had a piggy with ringworm and it looked rather like that only bigger! Hope you can get her to the vet before it gets worse!