I don't think too much of Stephanie J's response. Pets aren't disposable. No one will want a 17-year-old cat, and the poor thing would end up being euthanized in an unfamiliar place by an unfamiliar person.
Definitely take your cat to the vet to discuss the issue. The vet likely will ask: How long has your cat been exhibiting this behavior? Have you changed brands of food and/or kitty litter? Have there been any other changes in the environment (new/rearranged furniture etc)? How much is kitty eating/drinking? How much "output" is there in the litterbox?
It may be that whatever the underlying issue is, is treatable. You'll have to decide whether that treatment is practical and/or affordable.
It may be that the underlying issue is NOT treatable, and that your kitty's confusion or pain can't be effectively managed. In that case, euthanasia may be the most humane option. But it can be done while you're holding her, saying goodbye, instead of just dumping her as Stephanie J suggests.