http://www.drjwv.com/article.php?view=0004.phpI don't know the credentials of the writer of this website - but they suggest that there is currently no definitive blood test and a DNA test hasn't been developed so far. I would ask your vet to contact one of the vet colleges - whichever is local to you - to discuss it with them and see what else they can find out for you.
And as Westcoast said, discuss it with your girl's breeder - apart from anything else they need to know, since it appears to have a hereditary basis, and if they have been involved in the breed for a while, they should have some experience of it. I think there are actually some Sharpei breeders on here that might be able to help.