For a persistent dry cough that disrupts sleep, a generic cough suppressant (antitussive) like dextromethorphan can be very effective in quieting the cough reflex. If allergies or post-nasal drip are contributing to the irritation, an antihistamine like chlorpheniramine may also help. Since her symptoms have lasted five days without relief, it is highly recommended to consult a doctor. A physician can safely examine her chest to identify the underlying cause, such as a viral infection, asthma, or reflux, and prescribe stronger, targeted treatments if necessary. Meanwhile, sipping warm fluids and using a room humidifier can help soothe her throat.