I will try to help you to the best of what I have understood from your query. The query is bit ambiguous but this is what I feel is the problem.
I am sorry that your mother has been diagnosed with lung cancer
with also spots in brain and that it is in stage 4.
She has been a pot smoker for forty years in her life.
I am sorry but stage 4 lung cancer has very poor outcome. The 5-year survival rates in an advanced stage are very less.
She needs to quit using all forms of tobacco and pot too.
options are available. They can be decided upon individual patient needs and benefits.
I hope this helps you.