If it has been sneezing for longer than a few days you may have to take it to the vet to check that there is nothing stuck up its nose that is making it sneeze.
Like humans, cats can sneeze for several reasons...usually due to dust or other nasal irritants. If your cat is otherwise fine,I'd not worry too much. But if she's lethargic, not eating, or has discharge, she really should go to the vet.