A granuloma of the lung is not cancer. Granulomas are very common. It is a scar, from a lung infection that she had sometime in the past, most often an infection with a fungus or with tuberculosis. It may never go away and that is OK because, like any scar, it is nothing to worry about. In many instances, calcium, as found in bone, may deposit or accumulate in a granuloma and that is further evidence of the benign nature of the lesion.
She should probably discuss this further with the doctor who ordered the CT scan, along with the question of why the CT scan was ordered in the first place.