My female GSD has a skin issue? I don't know what it is?

I agree with the food thing, especially wheat grains can cause skin irritation. since it's between her legs where she can't lick, if it seems to be causing her discomfort or itching her you can put a little bit of a human cream (itch cream or pain cream) on it to relieve the discomfort. just make sure to watch her and make sure that she doesn't paw at it and then lick her paws.