In s01e01 : 25min45s, she comes back from the theater with the white dress and possibly white g-string under. Changes clothes and sits at the computer, I'm positive this is the white g-string in question.
http://www.imagebam.com/image/670155481282487
http://www.imagebam.com/image/c1fca6481282540
http://www.imagebam.com/image/670155481282487
http://www.imagebam.com/image/c1fca6481282540