I agree if a private is required to report to duty and he doesn’t then he is insubordinate. However, you just validated my argument...the difference between a lawful and unlawful order.
But again, Captain Rhodes has taken it upon herself to decide whether an order is lawful or not. The military does not take kindly to members who do that, and she can and should face a court martial if she refuses to report. Her position is no different than Michael New or Ehren Watada or any soldier or sailor who has been court martialed for refusing to report for duty in Iraq or Afganistan.