I'm guessing she's young based on this. Ask her if she is having bad dreams. Night terrors are terribly common amongst young children and can be very traumatizing. When this happens, just take the few minutes to ask her what's wrong. See if any of the basic solutions for kids work, such as night lights, teddy bears, and music.
She could try listening to some music before or while in bed. Most people would say calming music, but I, personally, find it annoying. Try something you both like listening to, or can at least agree on. Or invest in some headphones.
Also, eating before bed can cause problems sleeping, including nightmares and even sleep walking. Try to prevent her from eating for a couple hours before bed. Water and other non-sugary drinks are okay, but no food.
Another possible solution is watching a happy movie or show before bed. It has been proven that you are likely to dream about the last thing you were thinking about before falling asleep. It's hard to have a bad dream if you fall asleep while watching a Disney movie.
You could always try to get a different room, assuming you share one right now.