There is instinct. Duck, go that way, seek shelter. The feeling of 'should go, must go' in order to survive. It guides those who listen and insures survival. Without it many would be dead. Instinct fails.
It is sudden, one moment she is walking and the next on the ground, struggling to breathe. It is heavy, hot breath ruffling her neck fur. Kicking limbs make contact but seem to do nothing. Pain explodes in her side and her whirling eyes catch a flash of red and she can't watch, can't stand to see this grotesque thing on her belly and the - other. She twitches feebly, strength draining in the red beginning to stain the water.
It attacked without warning and she died without fanfare.