Suggest Remedies For Persistent Phlegm, Cough And Loss Of Voice

Hi Doctor,My 3 yr old girl has been fighting a cough and cold for 3 weeks now. First it started with hand, foot and mouth disease with high fever. Fever dissipated in few days but cough remained. After two weeks of cough her fever came back and she wad diagnosed with secondary pneumonia. She was given amoxycilin antibiotic and her fever dissapeared but her cough still remains. She still has a few days more to go on the antiobiotic dose. She had a chest xray last fridat that confirmed pneumonia and she was prescribed a 3 day course of predisolone to help with her phlem. Today is the 3rd day of the dose but she has been losing her voice and her cough and phlem is very much there. Are we missing something here? How worried should I be with her persistent phlem and cough and losing voice in an otherwise active kid?.