new 12 mm left hilar lymph node

Hi,

my question is my mother on aug 18 2008 had a left lower lobectomy and was in the earliest stages of lung cancer with not spread to lymph nodes and no per PET scan no other areas.  And did not have to have any further treatment such as radiation etc.  on Friday she had a repeat CT scan which shows only a what they state as a new 12 mm left hilar lymph node.  

of course since it is the weekend we have no spoken with her physician but are just curious if this sounds only like an infection or could if be the return of cancer. I know you cannot be precise but what is your opinion and should we be satified with the revealing of only infection and not further have it investigated?  Also is 12mm considered to be large?