After exhausting the vet services here we headed back to Sydney this week to see the ortho surgeon. After lots of x-rays and hip manipulation all he could say was the hip joint looks great and her flexion is fine. So he sent us away with a new NSAIDs and no answers.
I was just paying the exorbitant fee when he raced out saying he had an idea. Took her back in, he pushed her sacrum and whoa, she tried to bite him! So finally I have a diagnosis.