You didn't mention what stage the disease is. The fact that it is chemo and radiotherapy only which she had, it is stage 111 and above. correct me if i am wrong. If it is small cell lung cancer
, then the staging is different.
The new offer may or may not help. Only time will tell. But smoking
again will not make any difference to your mother present condition, so let her smoke. Unfortunately the damage is done already.
Lung cancer behaves differently in different people, perhaps due to the genetic factors, what it is called phenotype, but it will grow with time, unfortunately.