Complex sentence: The Predator attacks her, but just as it's about to kill her it notices a fetus inside her and lets her live, though the shock of the event causes her to pass out.
Split into simpler sentences: The Predator attacks her, but just as it's about to kill her it notices a fetus inside her. Seeing this, the Predator spares Leona, allowing her to live, though the shock of the event causes her to pass out.