The fiend does indeed go to open the door and, finding it locked, sighs and takes out a key, clicking it open. She then swings the door open and steps in, shutting it behind her carelessly - seeing as the door was locked, she isn't too careful (assuming Alaedra closed everything after opening them) and starts to pull her tunic off, lifting it up over her head. When it's just over her face is probably the ideal time to strike, so Alaedra is now entitled to a surprise round!