My mom has been taking nyquil for 5 days but with no relief to her cough. what should we do for her dry cough.

A Dr should see her: Older people can get worn out from things like persistent coughing, so have a doctor evaluate her asap. It could be a condition that requires an antibiotic or another prescription. Instructions on the bottle advice that and it's true. Hopefully, she'll feel better sooner. Thanks for being there for her - most parents wish for that!