Compare your ideas to these clips before you start surgery on your DD's motion. Windmill
Look at what each of these clips have in common with the hips and try to figure out how the arms clear the hips in the two more closed of these clips. I suggest it's not about the degree of closure but rather it's about the kinetic chain.
As to drills, I believe Ernie had it right when he told my DD to do windmill long toss. I'd suggest the same protocol Jaeger uses in his overhand long toss regimen. You can find a lot on that on youtube and google.