I think Gaga did the same position of the statue to create a real reflect on the gazing ball because if you look, the nails reflect is not the same of the statue. And the miror is to help her to have a good position. She always want to make the things perfectly ^^
I’ve always thought the artwork is Gaga herself, photoshopped to look like the statue. From the color to the precision (which isn’t present in the statue) to the similarity with the booklet images, I knew they photoshopped her to make her look like a statue. Thanks for pointing out.