Hi Louise,
I'm so sorry to your news about piper and can only imagine how upsetting it is for you both, I've had a quick look on the internet for you I know that you probably have already but I came across something about vitamin c being a miracle cure for HD, its " Ester C - miracle cure for Hip Dysplasia, " .its worth a look anyway.
Sending Piper a lovely big hug and my best wishes to you both,
Lizzy Molly and Evie