I have a couple of nine-year old hens, also a hen that's ten and one that's eleven. They are all showing signs of body parts slowing down and not functioning optimally. I myself have a growing list of body parts that either need kick starting with drugs or have quit working entirely. Old age is the pits. But no one, including chickens, usually specifically dies from it.
Usually what happens is that pathogens take advantage of lower functioning immune systems or organs cease to function. The trick is to figure out what we can do, if anything, to kick start your hen's works.
@microchick has pretty much nailed it. We can try to think of things to try to help your hen get right again, squeezing out a few more months or even years for her to have a happy life.
I had a young rooster many years ago with apparent cardio issues. He would have a seizure, almost pass out, flopping off his perch, and then miraculously recover. But it was alarming to watch. I started giving him one baby aspirin once a day, and he had no more seizures. Eventually, I quit giving the aspirin, thinking his problem was fixed. Then I found him dead under his perch one morning. Could he have lived longer if I'd continued the aspirin? Who knows?
I suggest you try the aspirin, and also give a B-complex each day to improve immune responses and circulation. Maybe throw in 400iu vitamin E, too. Heck, at age nine, it can't hurt, and if it works, hooray!