Very Smelly Maltese!?

My dog is 6 and a half years old... recently (within the past week) we have noticed a very strong foul odor coming off of her. I bathed her, and the smell returned within a few minutes. It's so strong, no matter how many times we bathe her. The scent is coming off her back, towards her tail. It smells like rotting, that's how terrible it is. She eats dry dog food prescribed by the vet (she has a weak stomach), with a little bit of chicken broth in it. Any suggestions would be appreciated!!!