Thanks for the information. There area few things to think about here. Although cancer in a 6 month old dog would be unlikely, stranger things have happened, so it still needs to be considered. An allergic reaction is possible, but it usually creates generalized swelling, not a white nodule. An abscess, either from an infection or foreign body is possible as well. A foreign body would be more likely than a bacterial infection. I am going to suggest something that is not seen or thought about often (including with myself). Oslerus osleri is a type of respiratory parasite that can create nodules in the trachea and lungs. It can cause a parasitic tracheobronchitis, and signs can look similar to a kennel cough or pneumonia. Usually, puppies are infected young by their mother. There isn't a lot about it on the web. This abstract might give you more inforamtion. It can be difficult to recover the larvae on a fecal exam. A transtracheal wash may help to get a diagnosis. I would probably start deworming with Panacur for 1 week and repeat in 3 weeks just in case. Having her airways scoped may be beneficial. Please let me know if you have any other questions. Hope this helps.