She is joined in her efforts by the source of the scream, who had enough wit in her blind panic to brace herself against the rail before the ferry began to tip. White-faced and trembling, Fifi becomes lucid enough in this moment to recognize that she's not alone; turning to see who's beside her, she abruptly wishes she were.
A lurch from their captor jolts her back out of her senses, and one thin hand snakes to grip the woman's wrist, either holding Wysteria fast to the railing or holding herself fast to Wysteria. Perhaps both.