To fetch or not to fetch...

Shayna is a 12 wk. old Scottie who sometimes brings me back
the ball.. sometimes she leaves it or only returns it half way to me.
But she always returns to me and I always give her a treat because
I want to reward her for coming back to me with or without the ball.
When she does bring it back I'm overjoyed and express that to her.

Am I on the right track or should I try something different?