Have you taken the dog to the vet for x-rays? An acute injury or panosteitis are probably at least as likely as HD at that age.
Please get her to see a vet next week. It's been going on for "a few months," so enough is enough. She needs an x-ray--you can't diagnose this with guesses from the Internet. If it's pano or an injury, your vet will be able to come up with supportive care. If it's HD, there may be surgical options -- or adequan therapy or other care. Whatever it is, if the dog's hurting, she needs care.