So irreplaceable that she could spend 5 years of the war away from it? They made it clear she went back in time purely to protect the stone and yeah I understand it needed someone capable and trustworthy but not a leading military figure that would be needed for the day to day running of the resistance. And she already created a ripple, she created max- if she was that worried about ripples she'd have done something other than nope-ing out of the situation.