My pup's on clindamycin drops after the vet diagnosed her w/ kennel cough.Now she's coughing up mucous.Worry?

My 3 month old, 3 1/2 pound silky terrier was diagnosed with kennel cough about a little over a week ago. At first, the vet put her on amoxycillin drops, but they weren't helping. She is now on clindamycin hydrochloride drops once a day. She is eating VERY well, playing VERY lively and other than coughing up some phlegm(a new symptom since being on clindamycin)she seems to be well. The cough isn't so much through the day unless she is lying down napping, but more in the evening and early morning. Is there anything safe to give her for the cough while she's on the clindamycin antibiotic. Thanks so much for your help.