Hello, firstly your mother looks like has nasal allergy. Pt with nasal allergy can have cough whenever the nasal secretions trickle down from back of nose to throat. As you have said maybe aggravated on dusting the bed. But in this age they can have gastric reflux causing dry irritating cough at night. Also pl check if she has headache, thick nasal discharge etc to see for sinus issues. She will need treatment for all this but only after an examination online or face to face
Next Steps
Consult ENT specialist online or face to face
Health Tips
1. For Gastric reflux, avoid late dinners, heavy meals, spicy oily food.
2. Let her take steam inhalation at night for nose/ sinus issue