This is most likely due to a tooth or gum related problem, it can be a case of gingivitis,oral ulceration, or even a lung or kidney disease. I suggest that you give a good look at your dog's teeth and gums and see if there are any signs of decay or inflammation of the gums. A good dog food to help with this if it is not tooth or gum related is Eukanuba Restricted-Calorie Rewards. That would also be helpful since you have her on a weight control type of food. I have listed some information below I feel will be helpful to you. But I suggest that you make an appointment with your veterinarian so they can give a full examination of the mouth, tooth and gum area and they may possibly want to try chlorhexidine, which is a mouth spray prescribed for a 7-14 day period to see if this helps with this condition. I hope this information will be helpful to you.
Halitosis, or bad breath, is an unpleasant odor coming from your dog's mouth. It’s more than just “doggie breath” in that it is offensive. Usually halitosis has oral causes, although sometimes it can be caused by other disease processes. These include: