The Name of the Star, by Maureen Johnson

YA paranormal. American Rory Deveaux from Louisiana is a student in a London boarding school, making friends and having crushes on cute English boys, when a near death choking experience leaves her with the ability to see ghosts. She is then initiated into an undercover group who seek ghosts to eliminate, and gets caught up in ghost Jack the Ripper's return to London to continue murdering women. It was almost as bad as it sounds.