desperate- odd problem with cat

I was given a 10-year-old spayed female cat around a month and a half ago.  Previous owner had had her all those years, said she'd recently developed the habit of peeing outside the litter box.  I haven't been able to get in touch with the person to ask if kitty was actually outside the box when this occurred, but what she's been doing here is standing up and spraying while in the box.  As it was a new behavior, previous owner assumed it was because their other cats were "bullying" her.  But after she was here a couple of weeks, she started doing the same thing here, and I have no other cats.  Before I agreed to take her, I asked previous owner if she might have a health/medical problem, but was told they took her to a vet and vet couldn't find anything wrong.   She seemed to settle in to new environment quite quickly and easily.  Because there are no other pets or people, she eats/drinks/uses box whenever she wants/needs, and sleeps whenever and wherever she chooses.  She doesn't play much, but when she does it's usually at night.  She seems content and communicative.   As this has been a new behavior (as previous owner said), and she's doing it here, too, there must be a cause and hopefully a solution.  Please advise...

Hello - and thank you for this fascinating question.  Urinating in the 'wrong' place can be a symptom of various different problems, and  detective work can be needed to get to the bottom of it.  It sounds as thought over-urination, in diseases such as diabetes, kidney disease and so on, has been ruled out, but your vet may suggest tests.  One under-rated cause is pain - mild arthritis or abdominal pain, which can make it difficult to fully squat.  This isn't always observed from watching the patient (- pain is notoriously difficult to spot in cats unless it is severe).  However if their hips aren't perfect, it can be hard to climb in and out of a box with a full bladder, or to aim it into a desirable spot.  Your vets might arrange trials with pain killers if this is a strong possibility.  If using a litter-box with high sides, switching for a shallower one can sometimes help.  Some cats dislike some trays and substrates (litter-types), so experimenting with different ones can be helpful.  Some cats will simply relax better if they are not overlooked.   Meanwhile, cystitis - inflammation of the bladder - is usually associated with stress which is increased in multi-cat households, because cats typically like their own territory.  Within a house, there will be a strict hierarchy as regards toilet habits.  Another cat using one's litter can put a sensitive cat off toileting completely.  Remedies for this can be as simple as removing an offending / stressful object (I knew one family who put a musical instrument down in the hall - and when it was there, the cat didn't use the tray).  Or as complex as rehoming that patient or another one of the colony to a single-cat family.   Please don't give up on this problem as cystitis can escalate.  The first thing to do may, however, be to make sure that the urine is not reflecting signs of kidney disease, stones, crystals and so on.    I also have some old blogs for your to read about various toileting problems.

• https://vethelpdirect.com/vetblog/2020/12/23/why-does-my-cat-have-bladder-trouble/
• https://vethelpdirect.com/vetblog/2019/01/18/cat-squatting-repeatedly/

... but because of the dangers of urine tubes blocking, would strongly recommend checking this out with your vet while the problem is still in its early stages.   I hope that something here is of use.

Because your household sounds very quiet and stable - and your vet sounds to have already checked the urine recently - do wonder about pain, or possibly lups or bumps in the bladder or tubes - in this case.