And, the moving boomerang is just a formality, once she has thrown it, then the person has already been hit. But, that person isn't another person, so she'd need to throw it at someone else to hurt them. It doesn't affect anything other than the target it has been thrown at, even if it forcefully bounces off an object. Thus, it makes no sound of impact when hitting something, nor is there a spark or chip. So yea, it retains kinetic energy until the impact with the intended target.