Is an infection that won't clear up an indication of the body shutting down?

Not necessarily, Globetrotter, but the fact that she's 94 means that her body just doesn't fight things off as well as it used to. I don't see where you've mentioned any other sort of health issues, but at 94, her immunity is just not what it once was, and it may not be possible for her to fight off these infections anymore. I wouldn't take it as a sign that the end is near - I've never heard of an eye infection ending someone's life unless it went untreated and ran rampant through their body, causing other problems. It sounds like she's getting the proper treatment, it's just that her body isn't responding like a younger person's would.