Shania Twain has been gearing up for the Las Vegas residency by sharing a number of nostalgic throwbacks on social media.MORE: Shania Twain brings the country glamour in gorgeous new photoThe latest picture posted on Instagram over the weekend delighted the star's fans after she chose to share an iconic image of her posing in the swimming pool wearing a mauve cowboy hat.In the image, Shania gazed into the camera, rocking a smokey eye, with her hair styled in loose waves.VIDEO: Shania Twain rocks