Yes, reward her with food, right next to your body so she has to come all the way to you to get it.
Well don't! If she doesn't bring the ball all the way back, game over. It sounds like she knows she doesn't have to, that you'll continue the game anyway.She has pretty good prey drive and loves playing fetch, but she does the same things with the ball when we play fetch! She only brings the ball 90% of the way. She listens when I tell her "off" and drops the ball.... but again, she doesn't come all the way and I have to walk up to her to pick up the ball...lol