I'm so sorry to hear about Penny, and being only 5mo, poor girl, I hope she is not in too much pain. Have you just suddenly notice her discomfort or has she been having difficulty for a while? I'm just wondering because if this is a sudden thing, maybe she has a tick?
Good thing you are going to your vet so you can discuss the symptoms and best possible solutions.
I have a 5yo GSD girl that has hip dysplasia, she was breed by a reputable breeder in Sydney that breed surveys their bitches etc, however dysplasia is just so rampart in GSDs that there is bound to be a dog with it in your dogs line. Lola has a score of 38 and is fairly even on both sides. To manage her, I give her human glucosamine & chondroitin and/or green lipped muscle products. She seems to be managing ok, but we will see how she goes as she gets older. Both her parents had excellent hip and elbow scores, however there would a gene in either her dam or sire and it has come through in Lola and one of her litter sisters. Reputable breeders do all they can to ensure they are breeding quality stock, but nothing is guaranteed and with dysplasia you have to look at environmental issues as well such as puppy being too overweight, too much excessive exercise etc as these can help contribute to the development of the dysplasia assuming the dog has the gene.
The puppy stage can be quite difficult, especially if you have a land shark, I use to use Vicks Vapourub on my hands and ankles to stop mine from biting me along with a gentle but firm correction, they hate the smell and it literally stops them in their tracks and then they will eventually grow out of biting, but remember the biting is good as she is learning bit inhibition, so long as you correct her or walk away from her (maybe not good for you though).
If you were to return her, and she does have dysplasia then they can't breed with her and would probably end up euthanising her, sorry to be blunt but I have been told by breeders they do enthanise a bitch if she can't be sold or breed from.
Best of luck and hopefully she will be well