My 21 Pound 9 Month Old Has A Bad Cough.

My 21 pound 9 month old has a bad cough. She is teething and every time she lays down to sleep the mucous is running down her throat and creating the barking cough. She wakes up so miserable if she gets any sleep at all. She is not wheezing or having trouble breathing just bad cough. Are there no expectorants that are safe for babies at her size/age? There are some homeopathic syrups out there for suppressants but my mother always said not to suppress the cough bc you want to keep it "open". Any ideas?