Have you tried to e-mail Best Friends...they work wonders with dogs...and have animal behaviorists on staff there....
go to bestfriends.org
look into their organization...it might help

or [email protected]
she is a good contact person.....

at least try for yours and Chewys' sake.....
aussies' are VERY nippy dogs by nature...they are Bred to Bite the heels of cattle...Heelers have the same issues....
perhaps,she is acting out her natural instincts....

maybe I'm grasping at straws....but a short e-mail couldn't hurt right?????

good luck....God Bless you and Dear Chewy