Okay, now this may come across as sexist, but it's a possibility: If they DO take a woman on board, or multiple women, being locked up for over 500 days, there's always a chance they'll throw regulations out the window and, well..... being pregnant several million kilometres from the nearest hospital can never end well for anyone. Besides, this is just an early-stage experiment - adding members of the other gender can cause more tension than a monogendered crew would experience, let's see if being isolated for 520 days is at all possible before complicating the situation any further.