Sounds weird but make sure her room is clean. When you wake up scared, seeing clutter, craziness, or weird toy shadows can make it worse.

Read VERY happy storied before bed. princesses and teddy bears and kitty cats. NO EVIL WITCHES GOBLINS OR MAYHEM!. Then you talk abotu the story for a minute or two. talk about how wonderful it would be to be a princess. Tell her to dream of the things she would do and tell her you can't wait to hear it in the morning. Send her to sleep with thoughts of rainbows and clouds and blowing bubbles. The cornier the better. The nightmares can cease or decrease with subconscious hints to dream of better things.