Hi, I'm Dr Steve. As dogs age they can develop body odors that can have different causes
It is common in older dogs t have bad breath and this can be caused by a buildup of tartar and calculi on the teeth as well as infected gums ( gingivitis) . If you look at her teeth if you see brown or gay buildup starting at the gumline and moving downtoward the tip of the teeth, that is Tartar and calculi. ALso if her gums , especially where the teeth join, are reddened, that is a sign of gingivitis. Both of these conditions cause bad breath and the bacteria present in the infected gums can cause the teeth to become loose and may fall out in time.
If she has these problems, she will need to have her teeth ultrasonically cleaned and antibiotics for infection. This would have to be done by your vet.
The gas problem is likely intestinal and even though she is eating a good quality food that she has been on for a long time, again as she ages her intestinal system may become more sensitive and she may benefit from a more easily and completely digestible food. THere are commercial diets available that are more digestible so there is ess by-product and less gas produced. Hills Sciencee diet has oone called i/d ( for intestinal diet) and one called "sensitive stomach" other brands will have similar products . I have my clients use a very high quality brand of food. Some of the less expensive ones use lower quality ingredients to keep the cost down and these lower quality ingredients are often not completely digestible and may not do what she needs.
THere is one other product that I have used for bad breath ( if her teethe are clean and if she doesnt have infected gums as I mentioned earlier) . THis is called Pet Sweet breath freshener and is added to the drinking water. If she does have tooth problems , then this product will not mask or help with bad breath. I hope this has helped. I will check throughout the day and evening to see if you have more questions. Thanks for your question and god luck .
sorry typo god=good.