To clarify, was there ANY discomfort on her arm? Pink skin on the forearm is very normal and suggests she is using good posture and feeling the whip. With some focus on improved posture and whip, I think she has a good foundation to build from. Start up close with quarter or half whips, with no emphasis on control. Give up control. The person standing in front of her has one job: Fetch (not catch.) Give the fetcher multiple balls to minimize chasing time. Close the eyes if needed. Throw into a net. Focus on staying stacked over the plant foot. Relax the lower arm and pull the ball into release. Let the ball whip out of the hand rather than trying to throw the ball to the glove of the fetcher. Use a camera (iPhone with slow mo) so she can self-evaluate. A cue I've borrowed from javasource is to imagine an eyeball on the drag knee that wants to see the fetcher.
