I have three cats.
Welcome to Cats & Kittens....
My first question is when was she at the vet last? At her age, a lot of vet recommend a visit every 6 months just to keep up with their health (the cat's health, not the vet - LOL). Usually the first thing I recommend when a litterbox issue turns up is a vet check. Cats are very good about hiding health issues but this is sometimes a first sign of something.
If not medical, then you are right and it is a behavior issue. It could be that she had been cornered in the box. Or, since she is older, is having problems getting in and out of the box. If it hurts for her to get over the edges, she may go somewhere else.
Hope that gives you someplace to start. Let us know how it goes....
Welcome to Cats and Kittens.
Well, my memory is faulty, Shadow's only about 13.
I hope that all comes back fine with her bloodwork.
The Feliway and catnip may work.
The bloodwork came back just fine.
That's good that her blood work came back fine.
You may have to confine her to a seperate room until you get a stool sample from her, unless you can watch her most of the time.