4 months is WAY to young for children cough medicine. At that age she needs to see her pediatrition if she has a bad cough. Coughs in infants can turn into something serious very fast if not looked into. There is also no over the counter medication for an infant that young for coughs and colds so she needs to see her doctor.
young cough medicine or take to the doctors may be throat infection
does she have a mucus build up or just coughing? dry heaving?
how old is she?
4 months almost