Take a breath and relax. I know that's pretty impossible right now, facing this kind of diagnosis for your mother. In 2008, my little brother, then 16, was diagnosed with bone cancer, primary tumor was in his knee. The prognosis was good unless it had spread to his lungs. If it had spread, then his chance of survival was more like 20%, not good. So after PET scans and such, it was found that he had a nodule on his lungs. My family was positively devastated.
He had to go through ten weeks of intensive chemotherapy before surgery and before they could truly assess the nodules in his lungs. After the grueling ten weeks was over, they did another PET scan, and the nodule was still there, completely unchanged, whereas the primary knee tumor had completely died.
The oncologist explained to us that the lung 'nodule' was not cancer at all, because if it had been cancer, it would have responded in kind to the chemo (like the primary tumor). My brother receives regular scans now that he is in remission (cancer free over three years now yay!), and the lung nodule remains unchanged.
The doctors told us that people can get scar tissue on their lungs from respiratory illnesses like asthma, pneumonia, etc. People can inhale foreign particles that embed themselves into the lining of the lungs. Smokers can develop scar tissue, etc., so it's not uncommon for there to be something on the lungs that shouldn't necessarily be there.
All of this to say, you don't have any answers yet, so don't hang your hat on the worst case scenario. After all, it could be absolutely nothing, and then you would have wasted all of this energy on such tragic thinking.
I don't know if you are a christian, but the power of prayer and positive thinking works miracles. I will never forget the woman who prayed with me after we learned of my brother's lung nodule. She told me, "Don't worry, it was just a mistake on the scan. There's no nodule." She absolutely believed that, and prayed on that. It was inspiring, even if I couldn't truly believe it myself at the time.
My deepest thoughts & prayers to you and your family!