Don't Look Down

When her sister dies after falling off a cliff where the railing had become loose, Carla has a hard time getting over the death, keeps having visions of her sister yelling at her for not saving her and develops a fear of heights.

Her therapist encourages her to join a class with other acrophobiacs, but the members of the group begin to die in similar ways - falling from heights.

Is someone after Carla and was the loose railing that killed her sister really meant for Carla?