If we make allowances for media misreporting, then perhaps it went along these lines:
She saw the guy while she was in bed, and then later tiptoed to the bedroom door and watched them leave. She could have heard him telling Elizabeth to be quiet or he'd kill her (Elizabeth), and mistaken it to be a comment directed to her. Fear of being seen (and killed) could have sent her back to her bed, where she remained quiet and still. After a long period of terrified silence, she finally crept to her parents' room, and spilled the beans.
The story is still plausible.