Please take your cat to the vet TODAY. Think of how horrible you're going to feel when you find out this is a totally treatable disease (like oh, maybe diabetes or hyperthyroid) and you could have saved your cat unnecessary suffering, or even saved her LIFE. As cats age (and yes, your cat could still have many years ahead of her with proper care), it's our responsibility to make sure they go for regular check-ups and that when anything is "off", we get them prompt veterinary attention.
Let us know what the vet says. There are plenty of people on this board that have tons of experience with all sorts of feline health issues and may be able to help you with treatment plans, etc.
"To close your eyes will not ease another's pain." ~ Chinese Proverb
“We must not refuse to see with our eyes what they must endure with their bodies.” ~ Gretchen Wyler