Exactly. She may seem ineffectual, as others have said, but in fact she's the only rational character in the film. (I don't remember her well enough in the book.) She's the stand in for the audience and reacts to the events at the hotel in a pretty realistic way. Wouldn't we all be freaked the fuck out by Jack's…

I agree. I loved the book. The movie completely missed the point of Serena the character and her desires, and drive and need to not just erase but annihilate her obstacles . And the ending with that panther! Ludicrous.