Not saying she could have stopped him, but she's a jounin and the village was being invaded. The least she could have done was cast a genjutsu or throw a kunai or something rather than act like a frightened little housewife.
Just cuz she was pregnant doesn't mean she can't cast some genjutsus? Besides, its a known fact that when you are pregnant you should be getting 30 mins of exercise per day anyway. The paths were all split up over various parts of the village, so she could have tried to genjutsu them one at a time and have some of the other people finish them off. again, not saying she could have done much, but she's the village's top genjutsu expert and a jounin she could have at least tried to do something.
i guess she doesn't have the will of fire.