Depending on the dog's circumstances prior to being adopted, it may take a while to housebreak her. My current 2 year old male rescue took 10 months! He was basically raised in a cage until he was about 6 months old. From that irresponsible owner/breeder he was moved to a boarding facility for a few more months, until a court released the 30 or so dogs for adoption. When I adopted him at 12 to 14 months old, he was not housebroken and hated being crated, becoming a skilled escape artist. This guy's "normal" was to live in his own waste.
A female I adopted at 3 or 4 years old took about a month to housebreak. Her background was a bit sketchy, but I don't think she had lived in a house before mine.
It can take a lot of patience, and I hope these adopters will stick with it and not give up on her. Has a veterinarian ruled out physical problems? BowWowMeow's suggestions should help a lot. (For the record, 4 other GSD's I adopted as adults had no problems with housebreaking.)