My Mom Said And I Over Heard "I Can't Breathe"

My mom said and I over heard "I can't breathe" and she does smoke she has went to a doctor first they made her take a CT scan and they could not find anything and they want to take another test but for her chest and not lungs but if they do to much she could get cancer and our family does not want that they said she might have namonya but I am worried