Have your child keep a small notebook and writing materials by her bed. In the morning or after she awakens from a bad dream, she can write about her dream. A kindergartener can draw a picture and you can write the words of what she said about it.
The more details the better! Who was in it? What happened? How did it make her feel? Your gentle and supportive questioning will help her to look at her fears more comfortably.
Later in the day both of you can think together to find out what might have caused a certain dream -- was it from a TV show? Fear of an upcoming event?
Sharing her dreams with you will make her feel more powerful over them. An old nightmare won’t be so scary anymore after putting it into words.