She is within a few hundreths of a second of releasing the ball. She has planted her stride foot and stopped her forward motion. After a legal drag, she is picking up her foot to allow her shoulders to come up and hips to close. Her foot will then set down to the side in a defensive position.
Legal. (At least based on this stop-motion photo.) But then we all know that nobody can be that good - so she must be illegal!
WMB