"Delicious B." <u22331@uwe> wrote :

If there is even a question about the box, keep it cleaner. You don't want
to get into a "pissing match" with a cat, pardon the pun. The cat always
wins. That said, we have a cat who has actually jumped on the bed and
peed on my husband when he upset her. :) He had been shooing her down
off the bed because he was washing his bedding, and continued to do so
until he got under the covers to go to sleep. Whereupon babygirl hopped
up on the fresh, clean duvet and peed all over it, with him under it.

I took her to the vet the next day, and he told me what I am telling you
now. We kept the box cleaner and avoided pissing her off, and she was
fine--until we relapsed and then she peed on the rug.

Important: use an enzymatic cleaner to get the pee smell out, once cats
start this they don't want to stop due to the scent. The chair now
smells like "toilet" to the cat. I sue one called Kids n Pets, it is the
best we have tried, and easy to use, too. Good luck. This is a dismaying
problem.

P.S. what has changed that might be upsetting her? Are you giving her
enough attention? Petting and play?

These links might help you.
http://www.fabcats.org/spraying.html

Housesoiling . A very thorough article by behaviourist
http://www.apbc.org.uk/article10.htm