She darted out and I didn’t notice until many hours later. She never made it back.
I’ve raised many a cat in my lifetime, and never had one that didn’t know that a litterbox was for.
Worse yet, I sometimes had a pet come inside the house and head for the litterbox. The whole outdoors was available, but they wanted the box instead. And no, I never encouraged or discouraged that attitude; it was just natural.
I have one now - I took in a feral cat about 18 months ago. I think at the time she was about nine months old. She’s never figured out the litter box. We have another cat that uses the litter box, but Sage just doesn’t get it. She goes outside. Sometimes she pees in our tub.
By the way, we also have a little terrier dog, whose favorite thing is to chase anything that moves, and is very aggressive. You’d think that a feral cat and and aggressive terrier dog would be like oil and water, but from the beginning they’ve been best buddies.
What you are describing is the classic symptoms of a urinary infection. Take her to the vet right away; it won’t cure itself, and you will not be able to curb her obnoxious habit with discipline. It’s often thought that, due to the infection and the cat having a hard time peeing, she thinks it is because of the place, so will try other places like tubs, beds and carpets. It’s really not her fault.
A 2-week antibiotic regimen should clear it up, but you must do it without delay.
My medical treatment info may be out of date. Maybe there is something better nowadays. The vet may also advise a low-ash diet.
Again, it’s usual but not universal. Just do a google search for folks who have had difficulty getting their kittens to use a litterbox. Sometimes you have to teach them that the box is the place.
Until this pair, it’s not a problem I’ve had to deal with. They’re getting much better, but every now and then I find a rogue poop or catch one pawing at the carpet. They’ve gone in for checkups every two weeks since I started fostering. They’re healthy. It’s just one of those things.
Urinary infections in cats are very common, especially social cats and outdoor cats.
Thanks for posting your experience, and the adorable pics. Your post reinforces what I’ve been thinking we might do once we move back to the US and are too old to adopt young pets. We can either adopt older animals, or foster. Or both 
I’ve been on vacation, and just now checked back in. I mentioned that this was a feral cat that we took in over 18 months ago, and she never learned how to use the litter box. There is no urinary tract infection, just that she doesn’t seem to understand the litter box and prefers to go outside. Sometimes she also pees in my bathtub.