I would recommend a vet visit and full bloods, especially with teh drinking, it could be a sign of something, but even if it is, it could be manageable. My old man Ginger never used to like using a litter tray and would rather hold it in for hours, but when he hit 14, he couldnt do that any longer, and I had to put a tray back down for him (the one the foster used wasn't good enough for him!!), so would definitely put a tray down, it is better to have a tray in the house anyway, you can keep an eye on what they are doing that way. Good luck with her, and tell her that 14.5 really isn't that old for a cat.