she is coughing for a reason so the first and most important step is to find that reason. does she have asthma? bronchitis/bronchiolitis? pneumonia? influenza? there are so many reasons. there are few if any recommended medicines for cough in children. some are expectorants that cause her to cough (probably not something you are interested in) but children (especially girls. don't ask me why) cannot hock up phlegm. there are cough suppressants but these may be contraindicated since the cause of the cough is not known. some people are safely using honey to quiet a cough and certainly a humidifier is helpful. my recommendation is for you to have her properly examined. while most causes are viral a few are bacterial and require antibiotics.
my daughter has a horrible cough. she is 5 years old. what can i give her?