Girls, could you please tell me how to be? My daughter has mucus build…

Girls, could you please tell me how to be? My daughter has mucus buildup in her throat while there's nothing in her nose and nothing leaks out. It's especially noticeable as it wheezes during sleep. We're using Acqualor drops, but there are no changes. The doctor just told us to do this. Someone suggests rinsing with saline or physiological solution, is it safe?