The situation you have described appears to be an incidental finding on the chest x-ray. This is a common occurrence. The cause may be a number of conditions but an old infection is probably the most likely reason. An old x-ray will be useful to compare to see if the spot was there previously. Tuberculosis can present in a variety of ways and if there is suspicion for this condition a number of tests like skin test for TB, sputum evaluation and certain blood tests will be needed. Old TB can present as a spot on the x-ray. The size of the spot also helps with the diagnosis. Serial imaging over a period of months to years will show if the spot is stable. A CT scan of the chest may help depending on the size seen on the x-ray. If there are no clinical symptoms like weight loss, loss of appetite, night sweats, productive cough - sputum, fever, etc it may be unlikely to be an active issue. Given the young age it appears less likely to be a cancer. In medicine there are many situations where there is no certainty in diagnosis but only a probability of the disease being present. However clinical evaluation, periodic assessment along with certain lab and imaging tests will help with the diagnosis. The situation with the incidental chest radiograph finding is the same in your friend and she should be evaluated by a pulmonologist to get a more definite conclusion. If there are no clinical signs of illness I do not see the x-ray finding preventing any travel or employment.