My suspicion is the problem does not have anything to do with a medical problem but a diet problem.  What I mean is - if you feed her table scraps to get her to eat, whenever you don't give her any, she refuses to eat and will hold off until you do or until you switch dog food.  The different food and/or adding wet food, is more 'tasty' at first, so she'll eat that for awhile, until she get's finicky and holds out for more table scraps or different food once again.  So the cycle continues.

At her age especially, it's very important her diet is well balanced and a quality brand of dog food is chosen - and you stick with it.  No table scraps needed.  You are going to have to be more stubborn than she is on this one!  I have NEVER seen a dog starve itself to death.  Eventually she will eat without anything added to her food.  And when she learns that's the way it has to be, she'll stick with the regular diet.  Her bowel movements will become more consistent and regular also - and this is an important part of her well being.

I promise she'll be a happier healthier dog if you go this route.  And you won't have to go through the inconvenience of having to continously prepare or switch foods - with the added comfort if she ever needed to be kenneled or hospitalized, she'll keep her strength by being able to eat 'just' dog food!

All of this aside, she is considered a senior and health concerns do need to be considered with food problems or not.  If she hasn't had a thorough exam including blood/urine testing in the past year, I highly suggest you make an appt to get this done.  Always best to rule on the side of caution when they get older!

I do wish you well,