Complex sentence: As she enters the living room, the door to the closet she found Nicole's phone in earlier opens and suddenly, she is knocked by an unknown force, which tries to pull her into the room before Annie manages to kick it shut.
Split into simpler sentences: As she enters the living room, she sees the same room where she found Nicole's phone open. Suddenly, she is knocked by an unknown force, which seems to be trying to pull into the room, before Annie manages to kick it shut.