We'd all like to do it like this. Here, Christine has turned her shoulders well beyond 90 degrees, yet she has maintained a compact arm swing. She is able to make that huge coil, but leave her left foot on the ground, and have minimal hip and leg motion.
For us mortals, let's try to turn as far as possible in the backswing, without lifting or shifting. This will allow us to hit crisper, more consistent shots.
WONG! at Impact
SMASH it. Christine is showing a quiet lower body/stable base, her left leg planted, and perfect "y" position with arms and club-shaft. Nice!