That IS a tough one!! I don't have much advice, but I did have a thought.....sometimes, things *begin* for one reason, but *continue* for a different reason. KWIM? The dream really DID scare her, and the concept of "it isn't real" must be sooo hard for her to grasp....but I think that perhaps what she is afraid of now is the *feeling* of being scared...does that make sense?
My dd is almost 3, and I have often in the past, when she gets hurt and is crying...been teaching her to "think happy thoughts". I will make my voice very quiet and breathy, and I will say "Let's think happy thoughts, like swimming at Mikey's house, and the kittens we saw at the pet store...can you name some more?" This only seems to work when we are close and cuddly and quiet. Don't know if it will work "in the moment", but maybe at bedtime after stories you could go through those visualizations with her, while adding "These are such happy thoughts....do you think we should think happy thoughts when we feel upset or sad?"
OR...dh just offered this....could you tell her "Guess what?
? That dream you had? That was Daddy!!! daddy came in here last week and was putting your clothes away, and he thought you were sleeping..." Then dh could say "I didn't mean to scare you, silly, I was just trying to be very quiet and not wake you up!"
Not sure how I feel about that, just kinda brainstorming for you!
My dd has Chritmas lights in her room, on top of her armoire, entwined in some berry garland. You can get a 30-light set especially now at holiday time....her room will glow, it really looks so pretty, and is just enough light to see, but not so much that a person couldn't go to sleep. . Maybe you could tell her they are fairy lights or something? I saw Super Nanny suggest that once, and I had to chuckle since my dd has had those in her room since moment one!