Yes, you can give her acetamenophen and cough syrup at the same time. YOu can also give her dark (buckwheat honey) which is very effective.

If you still want to give her a medicated syrup, I would suggest what would be most effective: a simple guifenisen medicine. You can give your child 10mg/kg/dose. This would be 4.5 mg of guifenisen per lb of body weight per dose, and you can give her 2-4 doses per day.

If her symptoms do not improve in a couple days or if she continues to run a fever, you will need to take her in to the doctor.