1. Please check for any arthritis near the joint she is licking at. Some dogs are painful, and start to self soothe by licking. Sometimes treating her with a pain medication like metacam helps with the accessory situation of a lick granuloma.
2. check her anal glands. Some dogs for some reason don't let you know that it's the anal glands that are bugging them, and they focus on the granuloma, which leads me to...
3. change food. There may be an underlying allergy that is causing her to itch, and in an older dog, they don't always have the physical ability to reach around and focus on their anus, which is what could be itching.
4. Increase her mental activity. Taking her out to different places, even just to poke around. This can be a boredom thing, too.
Clean the area with a broad spectrum type of cleanser, like peroxide often. The smell of bacteria from them licking, will cause them to lick, which builds bacteria, which smells, and it goes on and on.
Different products like bitter apple, etc. are ok to try, but I haven't had the best luck with it. sometimes bandaging the area, and keeping the bandage on for two weeks can give the area a chance to heal, but good luck if you have a life... keeping an eye on her 24/7 is not reasonable for most folks.
Let me know what you find out, as far as the arthritis, etc. That is usually a factor in these late onset situations.