The behavior may have been triggered by something she had either seen or TV or heard from other children.
Somethings to try-
About 30 min before bedtime, read a book to her about a strong girl that is able to battle (the things she's afraid of) You can make up the story yourself.
An hour before bed time, engage in a play that also allows her to combat "make belief" things that scare her. In her play, she would have to overcome these (with your help and encouragement)
You may want to at bed time use a lavender spray on her pillow and tell her that it wards off bad dreams.
Supplementing her with magnesium at bed time acts as a sleep aid and manages anxiety. Your pediatrician can tell you what dosage (unless it is already present in her multivitamin)
Encourage her during the day to tell you what is making her think these thoughts. They are anxiety provoking and the anxiety also has to be something to be looked into.
You want to engage her imagination (that is where the problems is stemming from) If you are not able to shape her behavior, see if she can talk to the school counselor or a behavioral modification therapist.