Plot hole: When Mr. Loren introduces his wife to everyone, he tells her, "You know Watson Pritchard of course." That can't be because at the beginning of the movie the characters are asking if any of them know Frederick Loren. No one personally knows him including Watson Pritchard. He says, "I don't know him, all the details about renting the house were done by mail." If that's the case, it's impossible for Annabelle to know Pritchard since Frederick invited all the guests without his wife's approval. (00:34:05)
Plot hole: Even if Dr. David Trent's and Annabelle Loren's elaborate plan had worked flawlessly (framing Nora Manning for Frederick Loren's death), the fact remains that they faked Annabelle's death for everyone to see, which would immediately arouse suspicions for investigators. Even if Annabelle and Dr. Trent somehow fled the scene before the police arrived the next morning, their actions would still raise many questions that implicated them; thus, their clumsy and convoluted scheme was far from being the "perfect crime" they imagined.
Chosen answer: As far as the "gliding in and out", Mrs Loren presumably uses the same body harness she used to fake her hanging. As to the rope... the film is deliberately ambiguous on whether or not the ghosts are real, as evinced by the drunk's last line in the movie; the rope trick is probably supposed to reflect this ambiguity despite being Mrs Loren's trickery.