If there's a change in behaviour, then she clearly isn't her usual self. It could be that she's had a scare and feels more comfortable on her own and weeing in the same spot. On the other hand it could be a health problem and for this reason I would get her checked out by the vet today. Cats are very good at hiding pain and sometimes the first sign is acting out of character. It could be she has injured herself (and it's not obvious) and therefore she doesn't want to come upstairs. Could be she's feeling uncomfortable and doesn't want company. Sometimes cats urinating in unusual places is a sign of a urinary problem. If she's urinating more it could again be a sign of a urinary problem, but given her age it's worth getting her checked out for diabetes and renal problems (which can be greatly helped if treated at an early stage).
Not sure how you can get a strain out of wooden floors, but you can buy urine eliminator sprays from pet shops and also surgical spirit helps breakdown the urine enzymes and the smell. If the rug is washable, use a biological powder as this destroys the urine scent and reduces the chance of them returning to that spot (they are often attracting back to a spot by the scent).
Have you tried putting a litter tray in the kitchen at night, or perhaps carrying her upstairs at bedtime and perhaps putting a litter tray on the landing where she can find it.
My parent's elderly cat used to re-mark the same spot when she had an accident. I think there would be a lingering smell, for her, in spite of the cleaning, but she possibly thought it was a safe place to go because she'd already been there IYSWIM.
Cats don't like the smell of citrus, so you could spray the rug with that, but if the problem is a continence issue, peeing is going to occur elsewhere, once that spot is no longer attractive.
Post in good housekeeping section for top cleaning tips.
Hopefully someone else will come along and give you better cat advice too, now the thread is bumped x
My lovely cat is about 12-13 years old and has always been very clean - uses cat flap and only had an accident once during a thunderstorm.
She has suddenly (literally overnight) stopped coming upstairs (used to sleep on our bed day and night) and is sleeping on the back of the settee.
She has wet on a rug several times and it has soaked through during the night and the wooden floor has turned black with the amonia. I have tried get-Off and white wine vinegar and water sprays but stains are really hard to remove. We've thrown 1 rug out and put a different one down.
We have put a cat litter tray down and she is using that - but still peeing on the rug as well. So we have started shutting her in the kitchen at night - but she appears to pee on the rug when we first get up and let her out. She goes out in the garden during the day.
Any ideas as to what we can do to 1. Get stains out of wooden floor 2. To work out why she is doing this.