My 8 Year Old Daughter Experienced A Nightmare About A

My 8 year old daughter experienced a nightmare about a month ago. In her dream, someone had left notes around our house claiming to harm us. Since then, she had frequent thoughts of the dream and becomes anxious. Most recently, she said she could hear her voice speaking loudly in her head as she thought about things. Any ideas as to cause for the voice? She is also just recovering from the flu virus last week.