There is no official protocol for the Vice President to salute as she is not in the military CoC, unlike the President who is, and that had not begun unlike the President Reagan years, as a sign of respect from their Commander.

Presidents, VPs, and those in civilian clothes aren't expected to return salutes -- Reagan was the first to do so. Later Presidents often followed the practice, though not always -- Trump mostly, but not always, saluted. VP Pence often did, not always. History of salutes: