The old adage that the left arm should always be kept straight is still as relevant as ever – as long as you interpret it correctly.
It does not mean that you must keep the arm absolutely ramrod straight and stiff, because that defeats everything. The object of the golf swing is to create the widest possible arc. That is impossible if the left arm is bent at any point in the backswing or downswing, and will result in a chopping action.

A high percentage of women who play golf slice the ball. As they near the top of the backswing, instead of continuing to swing the club back and to turn the shoulders they have a tendency to push their shoulders and arms up. Before they have completed their backswing they want to come down. If a woman gets sufficient shoulder turn then the club shaft at the top should be parallel to the line of play.