Make her a habit to brush her teeth twice a day (morning and night) with kid friendly toothpaste and simultaneously tongue cleaning as well.
Initially, kids refuse brushing but make sure to start putting paste just a dot amount and once she starts into the habit, slightly increase the paste amount a little bit more as per directions.
Next Steps
Even after proper brushing and tongue cleaning for a week , if still she has bad breath, get a Pediatric dentist opinion as well.