Welcome to the site. I am not a doctor but will answer this question to the best of my ability. There can be involvement in the lining of the lungs - the pleura. In a small number of patients a scarring occurs in the lungs, so-called fibrosis. This can be detected both clinically or on chest X-ray or scan. It produces shortness of breath, especially on exercise. Another rare manifestation of lupus in the lung is the so-called 'shrinking lung' where on chest X-ray the lung areas look smaller than normal. These are all signs of active disease and require treatment.
This information is widely available. You must both not worry that it is lupus related until you can get in with a lupus specialist and ask his/her advice. Nobody here will be able to advise you other than the same way as I am doing I am sure. We cannot comment on this type of thing in a medical way. Also there are different symptoms for different patients, so a good specialist must be sought here. The thing is though your sister must, I stress must, not just think she might have lupus, she really must look into these symptoms as soon as she possibly can.
Thank you for being such a good sister.