Have you checked her teeth and gums for any infection?
Dogs do vary in the amount of plaque they produce, some have food caught between and behind their teeth which over time causes nasties to form and a bad smell, generally fishy like. Brushing your dogs teeth generally keeps the breath nice and fresh and removes the plaque and bacteria build ups.
If the fishy breath continues though, might be an idea for a vet check sometimes underlying problems can also cause this smell respertory and nasal problems just being one. I take it she hasn't just emptied her anal glands and licked herself has she? Another option.
More likely it is just bacteria, so get the tooth brush out.