Pray with your daughter before she goes to sleep. Pray over her room and ask her guardian angel and God to keep her safe from the evil one. Children are VERY sensitive spiritually and need to be guarded, especially at young ages. My son had HORRIBLE night and daymares, and my older daughter has had trouble with bad dreams as well. If there is any unconfessed sin in the house, it has to be confessed. Pay attentino to what you see on TV, Radio, and what you allow into your house. Only put godly happy thoughts before yourself and your children. A lot of these nightmares are demonically induced.
A child can see something evil on TV and it can affect them for a long time. I'm an Orthodox Christian,(Orthodox Christianity is 2000 years old and still practices the same as at the time of Christ) and we have lots of icons (pictures that point to God and Christ) - pictures(icons) of Christ, Mother Mary, Guardian Angels. It really helped my daughter to always pray before bed, and also to have godly icons around her bed. These are very comforting to her, and also help her to visually focus on God, Christ and the saints. Now her nightmares are minimal. Just once in a while.
You can find out more about icons on goarch.org.