What a cutie!
So, was a consult with a specialist, an orthopedic surgeon?
I personally would think very strongly about an FHO. HD is very painful, and she is very young.
Do you have her on joint supplements? You want a good quality glucosamine and chondroitin supplement. I like to start with Cosequin, loading dose for quite awhile, and then note response. They can make a huge difference. When the HD is severe, sometimes you have to mix and match supplements, but start with this good quality one first.