Definitely see your vet, she is so young to be dealing with possible HD, poor girl. Hopefully you have a good vet and will be able to help you here.
She may have sprained her leg somehow and is now compensating for this injury, but your vet will be able to guide you better.
I have a GSD girl with HD, although is only mild, she has been scored and is pretty even on both sides. She bunny hops often and has difficulty getting up on a sofa or in the back of the car. To manage her, so far all I have done is give her human glucosamine and chondroitan capsules once a day, green lipped muscle powder once a day.
Your girl being a puppy, don't over exercise her, just gentle off lead (if you can) walking/trotting and allow her to stop when she has had enough. Don't allow her to run/sprint very fast with sudden stops like she would if you threw a ball fast. Keep her weight lean, don't allow her to become overweight.