My Cat Posie Sounds Congested Either In The Sinus Or Chest. She Is Sneezing And Has What Sounds Like A Cough. She Is Eating And Drinking. Could This Be A Common Cold?

Cats commonly get sick from feline upper respiratory complex.  This is often initiated by a viral infection but can progress to a bacterial infection.  The bacteria produce nasal discharge, mucous, and general malaise.  Viral infections tend to be self-limiting but the bacterial component often requires treatment.  
If you think the problem is in her chest or the cough is the main clinical sign then my concerns would be for a developing pneumonia or feline asthma.  This is more serious.
If this continues for more than 4-5 days or your pet stops eating/drinking, becomes lethargic, or starts sneezing mucous discharge have her examined by a veterinarian.  If the concern is related to the lower respiratory tract your cat will need x-rays.