See if there's a Chiropractor in the area that works on dogs.
We almost had to put our GR x GS to sleep one morning because it had got so bad, and at last minute, the vet suggested a show dog Chiropractor.. he was acting like a pup after his first visit!!
Sorry if I'm mistaken, but, she looks Border Collie to me.. if she is, go join and post about this in the Health Issues topic on a Border Collie Rescue board, similiar to this one..
http://bcrescue.org/phpbb2/index.php .. they can help you out with this and maybe help you help your pup's arthritis!!!