I am so sorry for not getting back to you sooner. I was out all day and just had a chance to sit down in front of the computer.
Your aunt probably did get a bit of her cranberry juice into her lungs, we call it "it went down the wrong pipe". Having said this, I do want to assure you that it absolutely doesn't mean she will get pneumonia.
When someone continuously aspirates food and drinks, eventually these particle will accumulate in some area in the lung and cause pneumonia but it usually doesn't happen from just one time. Your aunt probably aspirated a bit of juice, irritated her throat and has been coughing due to that irritation. It takes several days before pneumonia can even begin to set in which, I am sure, will not happen with your aunt.
There is no such thing as silent aspiration so I really don't think you need to be listening to your aunt's chest often. Her breathing rate is very normal, 12-14 per minute.
Signs and symptoms of aspirational pneumonia are cough with sputum, fever/chills (although it may not happen in elderly people), decreased appetite, increased sleep, increased shortness of breath. Aspirational pneumonia will not stay silent.
At this point there is not much you can do other then just observe her but again, I really do not think anything will happen.
Again, sorry for taking this long to get back to you.
Have a good night and let me know if you have any other questions.