polmonary embolism

My mom was recently rushed to hospital and they found out that she had a few blood clots on the lungs
so now she is on a blood thinner.  During all the tests they also found a very small spot on the lung
and today she went to the specialist.  He said it was a nodule. Is that a scar tissue? and how bad is that?
He wants to send her to get a PET scan, but she is really nervous and scared now, and starting to cry with fear
He said that it is really small and probably nothing, so why is he sending her for the PET scan.  She thinks
because he is doing that it is something to worry about.  She had to go to the hospital and have the lung test where
you blow into a tube yesterday but when we were at the specialist he didn't say anything about it and i forgot to ask as we were so overwhelmed with the PET scan.  I thought maybe the breath test came back good because i thought if it wasnt he would have said something wouldn't he have?
Can you please ease our minds?
thanks