Your mother has dry cough
for years !......daily or intermittently?
How was asthma
diagnosed? Did she undergo a lung function test? Asthma usually causes wheezing
, breathlessness and sticky phlegm.
Does the X-ray show lung scars? Upper lobe scars as well as diseases such as ILD cause chronic dry cough.
Details of history and reports needs to be communicated for a better advice.