First I would reassure her that you're there and that everything is fine now. Make it clear to her that it was JUST a scary dream, now it's over, and everything is okay. To help her feel more safe, it might be a good idea to check under the bed and the closet for "monsters". After that, you could read her a happy book.
try reading her a bed time story of something good.
Make the room less scary.
allow a pet to sleep next to her so she can feel protected when she has another dream the dog or cat will be by her side.
Good advice from Napp Ninjax and Chanelglit! A soft night-light might help, too. When I was young, I especially loved when my mother would sing me to sleep.