I wouldn't mind getting a handle on this myself. Everything is fine until you want to play ball with her or pick up something she knows is hers. She sounds like those sea gulls from Nemo! MINE MINE MINE. Its so hard to enjoy when all of a sudden she becomes this demented obsessive angel.
She barks the whole time you are getting ready to throw it or release it. LOUDLY! Any suggestions beside putting the ball away?