Don't try to just stop the symptom.

If your child is coughing, there must be something in her upper respairy system. The only thing you should do is helping her cough more and extude the sputum by spanking her back, from lower part of the chest to higher part. Never use any method to stop the coughing. I worked in ICU and some patients developed vital pnumonia finally because they did not cough well. Actually coughing is a self-protective action of our bady. If you can find any steam-making machine in store, buy one. Let her inspair the steam deeply then spank her chest, and then let her try her best to cough out the sputum.