She starts out forging, right out of the gate.
I hold it in my left hand up by my left shoulder, when I reward I say 'yes!' and drop it. I try to do that when she's not forging ahead, but back by my leg.
You may have accidentally created forging. I see it a lot especially when the toy is held at the front of the body - the dog wants to come forward and around so they can keep their eye on the toy. For a plain ball, I like to stow it in my armpit and the reward goes directly behind me. That way all the focus is on my direct side or behind me so there's no interest in being in front, if that makes sense?
For a dog that is a bad forger, I've also done the ball on the rope so I can sling the ball over my shoulder and have it resting on my back when not in use. That helps keep the focus off of my front side to prevent them wanting to swing out in front.
I'd suggest trying a new position for the ball, say tucked in the armpit, and start from a stand still. Practice a good solid starting position with the ball in the arm and practice delivering behind you. I like my dogs to almost anticipate stepping back to receive the ball.
I've found that practicing the start position tends to be skipped too quickly. You really want to nail it into his head that he will only get it at that exact position. When that's solid as concrete, it will be easier moving forward to reward for that exact position and build up the number of steps. When you start practicing going forward, the forging will be your indicator that either he does not know his position well enough or you've taken too many steps. Go back where he is successful, drill, then challenge.