Originally Posted by ALC
She is a strictly indoor cat and has regular vet checkups, so she doesn't have a tapeworm or anything of that sort that we can tell. We'll be taking her to the vet in a week or so, but I don't know if the vet will be able to shed any more light on this.
What do you all think could be going on?
When was her last check-up? Did she have a senior blood panel and a urinalysis done?
I'd be taking her to the vet sooner rather than later. Like today or tomorrow. Make sure she gets a full work up. There are a few things that could be going on here (diabetes, hyperthyroidism, IBD) but it's not likely dementia.
What is the special food she eats?
While you're waiting for the vet appointment, you might want to read this link on feline nutrition, and the important role it plays in various common health conditions (like the aforementioned diabetes): www.catinfo.org
In the meantime, please don't punish her anymore for doing something she clearly can't help. No more squirts with water, no more harsh tones or "tapping" on the bum. She may very well have a medical condition and your only going to add to her stress surrounding her insatiable appetite.